#include<iostream>

#include<cstdio>

#include<vector>

using namespace std;

const int N=1000005;

vector <int> wz[26];

int sum[N],ss,n,x,len[26],now;

char s1[N],s2[N];

long long ans;

void add(int i){for (;i<=n;i+=(i&(-i)))sum[i]++;}

int query(int i){for (ss=0;i;i-=(i&(-i)))ss+=sum[i];return ss;}

int main (){

	scanf ("%d%s%s",&n,s1+1,s2+1);

	for (int i=1;i<=n;++i)wz[s1[i]-'A'].push_back(i);

	for (int i=1;i<=n;++i){

		add(now=wz[s2[i]-'A'][len[s2[i]-'A']++]);

		ans+=i-query(now);

	}

	printf ("%lld",ans);

	return 0;

}