1 #include<cstdio>
  2 #include<cstdlib>
  3 #include<cstring>
  4 #include<iostream>
  5 #include<algorithm>
  6 #include<queue>
  7 using namespace std;
  8 #define Maxn 5010
  9 #define INF 0xfffffff
 10
 11 int mymax(int x,int y) {return x>y?x:y;}
 12 double mymin(double x,double y) {return x<y?x:y;}
 13
 14 struct node
 15 {
 16     int x,y,c,next;
 17 };
 18 node t[Maxn*2],eg[Maxn];
 19 int len=0,first[Maxn];
 20
 21 bool cmp(node x,node y) {return x.c>y.c;}
 22
 23 void ins(int x,int y,int c)
 24 {
 25     t[++len].x=x;t[len].y=y;t[len].c=c;
 26     t[len].next=first[x];first[x]=len;
 27 }
 28
 29 int st,ed;
 30 queue<int > q;
 31 int dis[Maxn];
 32 bool inq[Maxn];
 33
 34 void spfa()
 35 {
 36     while(!q.empty())
 37     {
 38         int x=q.front();
 39         for(int i=first[x];i;i=t[i].next)
 40         {
 41             int y=t[i].y;
 42             if(dis[y]>mymax(dis[x],t[i].c))
 43             {
 44                 dis[y]=mymax(dis[x],t[i].c);
 45                 if(!inq[y])
 46                 {
 47                     inq[y]=1;
 48                     q.push(y);
 49                 }
 50             }
 51         }
 52         inq[x]=0;q.pop();
 53     }
 54 }
 55
 56 int gcd(int a,int b)
 57 {
 58     if(b==0) return a;
 59     return gcd(b,a%b);
 60 }
 61
 62 int main()
 63 {
 64     int n,m;
 65     scanf("%d%d",&n,&m);
 66     memset(first,0,sizeof(first));
 67     len=0;
 68     for(int i=1;i<=m;i++)
 69     {
 70         scanf("%d%d%d",&eg[i].x,&eg[i].y,&eg[i].c);
 71     }
 72     sort(eg+1,eg+1+m,cmp);
 73     scanf("%d%d",&st,&ed);
 74     memset(dis,63,sizeof(dis));
 75     memset(inq,0,sizeof(inq));
 76     dis[st]=0;
 77     while(!q.empty()) q.pop();
 78     q.push(st);inq[st]=0;
 79     int a1=-1,a2;
 80     for(int i=1;i<=m;i++)
 81     {
 82         ins(eg[i].x,eg[i].y,eg[i].c);
 83         ins(eg[i].y,eg[i].x,eg[i].c);
 84         q.push(eg[i].x);q.push(eg[i].y);
 85         inq[eg[i].x]=inq[eg[i].y]=1;
 86         spfa();
 87         if(dis[ed]<INF)
 88         {
 89             // ans=mymin(ans,dis[ed]*1.0/eg[i].c);
 90             if(a1==-1||a1*eg[i].c>dis[ed]*a2) a1=dis[ed],a2=eg[i].c;
 91         }
 92     }
 93     if(a1==-1) printf("IMPOSSIBLE\n");
 94     else
 95     {
 96         int g=gcd(a1,a2);
 97         if(a2!=g) printf("%d/%d\n",a1/g,a2/g);
 98         else printf("%d\n",a1/g);
 99     }
100     return 0;
101 }