1 #include<cstdio>
  2 #include<iostream>
  3 #include<cstring>
  4 #include<algorithm>
  5 #include<queue>
  6 #include<set>
  7 #include<map>
  8 #include<stack>
  9 #include<time.h>
 10 #include<cstdlib>
 11 #include<cmath>
 12 #include<list>
 13 using namespace std;
 14 #define MAXN 200100
 15 #define eps 1e-5
 16 #define For(i,a,b) for(int i=a;i<=b;i++)
 17 #define Fore(i,a,b) for(int i=a;i>=b;i--)
 18 #define lson l,mid,rt<<1
 19 #define rson mid+1,r,rt<<1|1
 20 #define mkp make_pair
 21 #define pb push_back
 22 #define cr clear()
 23 #define sz size()
 24 #define met(a,b) memset(a,b,sizeof(a))
 25 #define iossy ios::sync_with_stdio(false)
 26 #define fre freopen
 27 #define pi acos(-1.0)
 28 #define inf 1e9+9
 29 #define Vector Point
 30 const int Mod=1e9+7;
 31 typedef unsigned long long ull;
 32 typedef long long ll;
 33 typedef pair<int,int> pii;
 34 typedef pair<ll,ll> pll;
 35 int dcmp(double x){
 36     if(fabs(x)<=eps) return 0;
 37     return x<0?-1:1;
 38 }
 39 struct Point {
 40     double x,y;
 41     int id;
 42     int pre,nxt;
 43     Point(double x=0,double y=0) : x(x),y(y) {}
 44     Point operator - (const Point &a)const{ return Point(x-a.x,y-a.y); }
 45     Point operator + (const Point &a)const{ return Point(x+a.x,y+a.y); }
 46     Point operator * (const double &a)const{ return Point(x*a,y*a); }
 47     Point operator / (const double &a)const{ return Point(x/a,y/a); }
 48     bool operator < (const Point &a)const{    if(x==a.x) return y<a.y;return x<a.x; }
 49     bool operator == (const Point &a)const{ return dcmp(x-a.x)==0 && dcmp(y-a.y)==0; }
 50     void read(int iid=0) { scanf("%lf%lf",&x,&y);id=iid; }
 51     void out(){cout<<"Bug: "<<x<<" "<<y<<endl;}
 52 };
 53 inline double Cross(Vector a,Vector b) { return a.x*b.y-a.y*b.x; }
 54 inline double Dot(Vector a,Vector b) { return a.x*b.x+a.y*b.y; }
 55 inline double dis(Vector a) { return sqrt(Dot(a,a)); }
 56 int ConvexHull(Point *p,int n,Point *ch){
 57     int m=0;
 58     sort(p,p+n);
 59     For(i,0,n-1){
 60         p[i].id=i;
 61         while(m>1 && Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
 62         ch[m++]=p[i];
 63     }
 64     int k=m;
 65     Fore(i,n-2,0){
 66         while(m>k && Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
 67         ch[m++]=p[i];
 68     }
 69     if(n>1) m--;
 70     return m;
 71 }
 72 inline bool Onsegment(Point a,Point b1,Point b2){
 73     return dcmp(Cross(b1-a,b2-a))==0 && dcmp(Dot(b1-a,b2-a))<0;
 74 }
 75 bool Intersect_Segm_Segm(Point a1,Point a2,Point b1,Point b2){
 76     if(a1==b1 || a1==b2 || a2==b1 || a2==b2) return 1;
 77     if(Onsegment(a1,b1,b2) || Onsegment(a2,b1,b2)) return 1;
 78     double c1=Cross(a2-a1,b1-a1),c2=Cross(a2-a1,b2-a1);
 79     double c3=Cross(b2-b1,a1-b1),c4=Cross(b2-b1,a2-b1);
 80     return dcmp(c1)*dcmp(c2)<0 && dcmp(c3)*dcmp(c4)<0;
 81 }
 82 Point Intersect_Line_Point(Point p,Vector u,Point q,Vector v){
 83     Vector w=p-q;
 84     double t=Cross(v,w)/Cross(u,v);
 85     return p+u*t;
 86 }
 87 int vis[MAXN],vvis[MAXN];
 88 int tcnt;
 89 int tConvexHull(Point *p,int n,Point *ch){
 90     int m=0;
 91     sort(p,p+n);
 92     For(i,0,n-1){
 93         if(vis[p[i].id]) continue;
 94         while(m>1 && Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
 95         ch[m++]=p[i];
 96     }
 97     int k=m;
 98     Fore(i,n-2,0){
 99         if(vis[p[i].id]) continue;
100         while(m>k && Cross(ch[m-1]-ch[m-2],p[i]-ch[m-2])<=0) m--;
101         ch[m++]=p[i];
102     }
103     if(ch[0]==ch[m-1]) m--;
104     For(i,0,m-1){
105         if(vvis[ch[i].id]) tcnt++;
106     }
107     return m;
108 }
109 ll n;
110 Point ch[MAXN],p[MAXN],stk[MAXN];
111 int solve(){
112     scanf("%lld",&n);
113     tcnt=0;
114     met(vis,0);
115     met(vvis,0);
116     For(i,0,n-1) p[i].read(i);
117     int m=ConvexHull(p,n,ch);
118     For(i,0,m-1) vvis[ch[i].id]=1;
119     if(n==1) return puts("0/1");
120     ll ans=m*1LL*(n-m);
121     if(m%2==0){
122         For(i,0,m-1){
123             vis[ch[i].id]=1;
124             i++;
125         }
126         ans+=tConvexHull(p,n,stk);
127         met(vis,0);
128         For(i,1,m-1){
129             vis[ch[i].id]=1;
130             i++;
131         }
132         ans+=tConvexHull(p,n,stk);
133     }else{
134         For(i,2,m-1){
135             vis[ch[i].id]=1;
136             i++;
137         }
138         ans+=tConvexHull(p,n,stk);
139         met(vis,0);
140         For(i,1,m-1){
141             vis[ch[i].id]=1;
142             i++;
143         }
144         ans+=tConvexHull(p,n,stk);
145         met(vis,0);
146         vis[ch[0].id]=1;
147         ans+=tConvexHull(p,n,stk);
148     }
149     ans+=m*1LL*(m-1)-tcnt;
150     ll cnt=__gcd(ans,n);
151     ans/=cnt;
152     n/=cnt;
153     printf("%lld/%lld\n",ans,n);
154 }
155 int main(){
156 //  fre("in.txt","r",stdin);
157     fre("average.in","r",stdin);
158     fre("average.out","w",stdout);
159     int t=1;
160     solve();
161     return 0;
162 }