#pragma GCC optimize("Ofast")
#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cassert>
#include <chrono>
#include <random>
#include <set>
#include <utility>
#include <array>
#include <bitset>
#include <unordered_set>
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}
inline double time() {
    return static_cast<long double>(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()) * 1e-9;
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n; cin >> n;
    string s; cin >> s;
    ll res = 0;
    ll jres = 0, ores = 0, ires = 0;
    ll jcnt = 0, icnt = 0;
    for (int i = 0; i < n; ++i) {
        if (s[i] == 'I') icnt += 1;
    }
    for (int i = 0; i < n; ++i) {
        if (s[i] == 'J') jcnt += 1;
        else if (s[i] == 'I') icnt -= 1;
        else {
            jres += icnt;
            ires += jcnt;
            res += icnt*jcnt;
        }
        ores = max(ores, icnt*jcnt);
    }
    cout << res+max({jres,ores,ires}) << endl;
}