#include <bits/stdc++.h>
using namespace std;
#define kien long long
#define FOR(i, a, b) for (int i = a;i <= b; i++)
#define FORD(i, a, b) for (int i = a;i >= b; i--)
#define pb push_back
#define pii pair <int, int>
const int MXN = 2e5 + 5;
kien ans, n, pi[MXN], pj[MXN], po[MXN];
kien dp[MXN], dp1[MXN];
map <pii, int> pp;
main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cin >> n;
string s; cin >> s;
FOR (i, 0, s.size() - 1) {
if (i >= 1)
pi[i] = pi[i - 1], pj[i] = pj[i - 1], po[i] = po[i - 1];
if (s[i] == 'J') pj[i]++;
else if (s[i] == 'O') po[i]++;
else if (s[i] == 'I') pi[i]++;
dp[i] = abs(pi[i] - po[i]);
dp1[i] = abs(pj[i] - po[i]);
}
FOR (i, 0, s.size() - 1) {
int kk = pp[{dp[i], dp1[i]}];
if (kk != 0) {
ans = max(ans, 1LL * (i - kk));
}
else
pp[{dp[i], dp1[i]}] = i;
}
cout << ans;
}