#include <bits/stdc++.h>
using namespace std;
void fastIO(){ios_base::sync_with_stdio(false),cin.tie(0);}
#define int long long
const int MAXN = 200'020;
int N;
int scroll[MAXN];
map<pair<int,int>,int> idxDiff;
int ans = 0;
signed main() {
fastIO();
cin >> N;
for (int i = 0; i < N; i++) {
char on;
cin >> on;
if (on == 'J') {
scroll[i] = 0;
}
else if (on == 'O') {
scroll[i] = 1;
}
else {
assert(on == 'I');
scroll[i] = 2;
}
}
vector<int> cnt(3,0);
idxDiff[{0,0}] = -1;
for (int i = 0; i < N; i++) {
cnt[scroll[i]]++;
pair<int,int> add = {cnt[0]-cnt[1], cnt[1]-cnt[2]};
if (idxDiff.find(add) == idxDiff.end()) {
idxDiff[add] = i;
}
pair<int,int> fnd = {cnt[0]-cnt[1], cnt[1]-cnt[2]};
auto idxId = idxDiff.find(fnd);
if (idxId != idxDiff.end()) {
int idx = idxDiff[fnd];
ans = max(ans, i - idx);
}
}
cout << ans << "\n";
}
