1 #include<cstring>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #define rep(i,l,r) for (int i=(l); i<=(r); i++)
 5 using namespace std;
 6
 7 const int N=200010;
 8 int K,m,na,nb,n,d,ans,lg[N],h[N],c[N],x[N],y[N],sa[N],rk[N],st[N][20];
 9 char s[N],A[N],B[N];
10
11 bool Cmp(int a,int b,int l){ return y[a]==y[b] && y[a+l]==y[b+l]; }
12
13 void getSA(int m){
14     memset(y,0,sizeof(y));
15     rep(i,0,m) c[i]=0;
16     rep(i,1,n) c[x[i]=s[i]]++;
17     rep(i,1,m) c[i]+=c[i-1];
18     for (int i=n; i; i--) sa[c[x[i]]--]=i;
19     for (int k=1,p=0; p<n; k<<=1,m=p){
20         p=0; rep(i,n-k+1,n) y[++p]=i;
21         rep(i,1,n) if (sa[i]>k) y[++p]=sa[i]-k;
22         rep(i,0,m) c[i]=0;
23         rep(i,1,n) c[x[y[i]]]++;
24         rep(i,1,m) c[i]+=c[i-1];
25         for (int i=n; i; i--) sa[c[x[y[i]]]--]=y[i];
26         rep(i,0,n) y[i]=x[i]; p=1; x[sa[1]]=1;
27         rep(i,2,n) x[sa[i]]=Cmp(sa[i],sa[i-1],k)?p:++p;
28     }
29 }
30
31 void getH(){
32     rep(i,1,n) rk[sa[i]]=i; int k=0;
33     rep(i,1,n){
34         for (int j=sa[rk[i]-1]; j+k<=n && i+k<=n && s[i+k]==s[j+k]; k++);
35         h[rk[i]]=k; if (k) k--;
36     }
37 }
38
39 void init(){
40     lg[1]=0; rep(i,2,n) lg[i]=lg[i>>1]+1;
41     rep(i,1,n) st[i][0]=h[i];
42     rep(i,1,19) rep(j,1,n-(1<<i)+1) st[j][i]=min(st[j][i-1],st[j+(1<<(i-1))][i-1]);
43 }
44
45 int lcp(int l,int r){
46     int x=rk[l],y=rk[r+na+1];
47     if (x>y) swap(x,y);
48     x++; int t=lg[y-x+1];
49     return min(st[x][t],st[y-(1<<t)+1][t]);
50 }
51
52 void col(int l,int r){ l=max(l,d); r=min(r,nb); c[K-(na-(l-d+1))+1]++; c[K-(na-(r-d+1))+2]--; }
53
54 void dfs(int x,int y,int z){
55     int t=lcp(x,y); x+=t; y+=t;
56     if (x>na || y>nb){
57         int c=K-z-(na-x+1);
58         if (c>=0) col(y-1-c,y-1+c);
59         return;
60     }
61     if (z==K) return;
62     dfs(x+1,y,z+1); dfs(x,y+1,z+1); dfs(x+1,y+1,z+1);
63 }
64
65 int main(){
66     freopen("bzoj4340.in","r",stdin);
67     freopen("bzoj4340.out","w",stdout);
68     scanf("%d%s%s",&K,A+1,B+1); m=2*K+1;
69     na=strlen(A+1); nb=strlen(B+1);
70     rep(i,1,na) s[++n]=A[i]; s[++n]='#';
71     rep(i,1,nb) s[++n]=B[i];
72     getSA(300); getH(); init();
73     for (d=1; d<=nb; d++){
74         rep(j,1,m) c[j]=0;
75         dfs(1,d,0);
76         rep(j,1,m){
77             c[j]+=c[j-1];
78             if (c[j]) ans++;
79         }
80     }
81     printf("%d\n",ans);
82     return 0;
83 }