#include<bits/stdc++.h>
using namespace std;
#define fast ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define ll long long int
const ll N = 100+5 , INF = 1e18 , MOD = 1e9+7;
void solve(){
ll n;
string s;
cin >> n >> s;
s = ' '+s;
ll cj = 0 , ci = 0 , co = 0;
map<pair<ll,ll>,ll> m;
m[make_pair(0,0)] = 0;
ll ans = 0;
for(ll i = 1; i <= n; i++){
if(s[i] == 'J') cj++;
else if(s[i] == 'O') co++;
else ci++;
if(m.find(make_pair(cj-co,cj-ci)) == m.end()) m[make_pair(cj-co,cj-ci)] = i;
else ans = max(ans,i-m[make_pair(cj-co,cj-ci)]);
}
cout << ans;
}
int main(){
fast;
ll tc = 1;
// cin >> tc;
while(tc--) solve();
return 0;
}
