#include <bits/stdc++.h>
using namespace std;
const int N = 2e5+10;
int J, O, I;
map<int, map<int, map<int, int>>> mp;
int main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n;
string s;
cin >> n >> s;
s = '.'+s;
int ans = 0;
for(int i = 1; i <= n; ++i){
J += (s[i] == 'J');
O += (s[i] == 'O');
I += (s[i] == 'I');
int d1 = J-O, d2 = O-I, d3 = I-J;
if(d1 == 0 && d2 == 0 && d3 == 0){
ans = max(ans, i);
}else if(mp[d1][d2][d3] == 0){
mp[d1][d2][d3] = i;
}else{
ans = max(ans, i-mp[d1][d2][d3]);
}
}
cout << ans << '\n';
}
