#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 5e5+10;
int k;
char str[N],c1,c2;
LL s[N];
int main(){
cin>>k>>str+1>>c1>>c2;
int n = strlen(str+1);
for(int i=1;i<=n;i++){
if(str[i] == c1) s[i] = s[i-1] + 1;
else s[i] = s[i-1];
}
LL cnt = 0;
for(int i=n;i>=1;i--){
if(i>=k && str[i] == c2){
cnt += s[i-k+1];
}
}
cout<<cnt<<endl;
return 0;
}