//找到a长度大于4右边b的数量
#include <iostream>
#include <cstring>
#include <map>

using namespace std;

typedef long long LL;

const int N = 5e5+10;
map<int,int>m;

int main()
{
    int k;
    char a,b;
    string s;
    cin>>k>>s>>a>>b;
    LL sum=0;
    for(int i=s.size()-1;i>=0;i--)
    {
        if(s[i]==b) m[i]=++sum;
        else m[i]=sum;
    }
    LL ans=0;
    for(int i=0;i<s.size()-1;i++)
        if(s[i]==a)
            ans+=m[i+k-1];
    cout<<ans;
    return 0;
}