#include <iostream>
#include <math.h>
#include <vector>
#include <string>
#include <algorithm>
#include <queue>
#include <stack>
#include <map>
#include <cstring>
#include <iomanip>
#include <set>
#include <bitset>
#define int long long
using namespace std;
using ll = long long;
using pii = pair<int,int>;
using piii = tuple<int,int,int>;
#define endl '\n'
#define f first
#define s second
int const N = 1e6+10;
int fenwick[N];
int si;
void add(int id){
for (;id <= si;id += id&-id) fenwick[id] += 1;
}
int sum(int id){
int sum = 0;
for (;id > 0;id -= id&-id) sum += fenwick[id];
return sum;
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int n;cin >> n;
string st1;
string st2;
cin >> st1 >> st2;
queue<int> mp[28];
vector<int> vc;
for(int i{};i < n;i++){
mp[st1[i]-'A'].emplace(i);
}
for(int i{};i < n;i++){
vc.emplace_back(mp[st2[i]-'A'].front());
mp[st2[i]-'A'].pop();
}
int ans = 0;
si = pow(2,ceil(log2(n)));
for(int i{};i < n;i++){
ans += i-sum(vc[i]+1);
add(vc[i]+1);
}
cout << ans;
}
