#include<bits/stdc++.h>
#include<vector>
using namespace std;
typedef long long ll;

int k;
string s;
char c1,c2;

int main()
{
	ios::sync_with_stdio(0);cin.tie(0);
	
	cin>>k>>s>>c1>>c2;
	int sum_c1 = 0;
	int n = s.size();
	ll ans = 0;
	for(int i = k-1,j = 0;i<n;++j,++i)
	{
		if(s[j] == c1)
		{
			++sum_c1;
		}
		if(s[i]==c2)
		{
			ans += sum_c1;
		}
	}
	cout<<ans<<endl;
	
	return 0;            
}