#include<bits/stdc++.h>
using namespace std;
#define task "a"
#define se second
#define fi first
#define ll long long
#define ii pair<int, int>
const long mxN = 2e5 + 7;
char chr[4] = {'J', 'O', 'I'};
int cnt[4];
map<ii, int> m;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
//freopen(task".INP", "r", stdin);
//freopen(task".OUT", "w", stdout);
int n;
string s;
cin >> n;
cin >> s;
s = '0' + s;
m[{0, 0}] = 0;
int ans = 0;
for (int i = 1; i <= n; i++)
{
for (int j = 0; j < 3; j++)
cnt[j] += (chr[j] == s[i]);
ii tmp = {cnt[0] - cnt[1], cnt[0] - cnt[2]};
if (m.count(tmp))
ans = max(ans, i - m[tmp]);
else
m[tmp] = i;
}
cout << ans;
}
