#include <bits/stdc++.h>
#define MAX 300000
using namespace std;
typedef array<int, 3> tp;
int S[MAX];
map<tp, int> mp;
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
int N, res = 0, X;
tp C = {0, 0, 0};
string s;
cin >> N >> s;
for (int i = 1; i <= N; i++) {
if (s[i - 1] == 'J')
S[i] = 0;
else if (s[i - 1] == 'O')
S[i] = 1;
else
S[i] = 2;
}
mp[{0, 0, 0}] = 0;
for (int i = 1; i <= N; i++) {
C[S[i]]++, X = min({C[0], C[1], C[2]});
C[0] -= X, C[1] -= X, C[2] -= X;
if (mp.find(C) != mp.end())
res = max(res, i - mp[C]);
else
mp[C] = i;
}
cout << res << '\n';
return 0;
}
