//Q
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
char c1,c2;
string s;
int main()
{
ll k,n,num=0,ans=0;
cin>>k;
cin>>s>>c1>>c2;
n=s.size();
for(int i=0,j=k-1;j<n;i++,j++)//不是i小于n!
{
if(s[i]==c1) num++;
if(s[j]==c2) ans+=num;
}
cout<<ans<<endl;
return 0;
}