#include <bits/stdc++.h>
#define int long long
using namespace std;
const int mx = 1e5+5;
int n;
string st;
int pre[mx], suf[mx];
int cnt(string st) {
int cj = 0, co = 0;
int ans = 0;
for (int i=0;i<st.size();i++) {
if (st[i] == 'J') cj++;
else if (st[i] == 'O') co+=cj;
else ans += co;
}
return ans;
}
signed main() {
cin >> n;
cin >> st;
int ans = max(cnt("J"s+st), cnt(st+"I"s));
int ct = cnt(st);
for (int i=1;i<=n;i++) {
pre[i] = pre[i-1] + (st[i-1]=='J');
}
for (int i=n;i>=1;i--) {
suf[i] = suf[i+1] + (st[i-1]=='I');
}
for (int i=1;i<=n;i++) {
ans = max(ans, ct + pre[i-1] * suf[i]);
}
cout << ans << "\n";
}
