#include<cstdio>

#include<queue>

using namespace std;

#define N 1000001

typedef long long ll;

queue<int>qs[26];

ll ans;

int n,A[N];

char a[N],b[N];

int d[N];

void Update(int p){for(;p<=n;p+=(p&(-p))) ++d[p];}

int Query(int p){int res=0; for(;p;p-=(p&(-p))) res+=d[p]; return res;}

int main()

{

	scanf("%d%s%s",&n,a+1,b+1);

	for(int i=1;i<=n;++i) qs[b[i]-'A'].push(i);

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

	  {

	  	A[i]=qs[a[i]-'A'].front();

	  	qs[a[i]-'A'].pop();

	  }

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

	  {

	  	Update(A[i]);

	  	ans+=(ll)(i-Query(A[i]));

	  }

	printf("%lld\n",ans);

	return 0;

}