#include <bits/stdc++.h>
using namespace std;
#define ll long long
int main(){
vector<ll> O, S, N;
ll n, ans = 0; cin >> n;
for (ll i = 0; i < n; ++i){
char huruf;
cin >> huruf;
if (huruf == 'O') O.push_back(i);
else if (huruf == 'S') S.push_back(i);
else N.push_back(i);
}
ll bn = N.size();
for (ll s : S){
ll p = upper_bound(O.begin(), O.end(), s) - O.begin();
ll q = lower_bound(N.begin(), N.end(), s) - N.begin();
ans += p * (bn - q);
}
cout << ans;
}
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