#include <bits/stdc++.h>
using namespace std;

const int N = 9 + 1e6;
const int oo = 7 + 1e9;

map<pair<int, int>, int> m;

void SaKaTa()
{
    int n;
    cin >> n;
    string s;
    cin >> s;
    pair<int, int> FIND(0, 0);
    m[FIND] = -1;
    int ans = 0;
    for (int i = 0; i < s.size(); i++)
    {
        if (s[i] == 'J') ++FIND.first, ++FIND.second;
        else if (s[i] == 'O') --FIND.first;
        else --FIND.second;
        if (m.count(FIND)) ans = max(ans, i - m[FIND]);
        else m[FIND] = i;
    }
    cout << ans;
}

int32_t main()
{
#define TASKNAME "FINDS"
    cin.tie(0)->sync_with_stdio(0);
    if (fopen(TASKNAME ".inp", "r"))
    {
        freopen(TASKNAME ".inp", "r", stdin);
        freopen(TASKNAME ".out", "w", stdout);
    }
    int testcase = 1;
    //    scanf("%d", &testcase);
    while (testcase--)
        SaKaTa();
    return 0;
}