#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
typedef pair<int, int> ii;
const int mod = 1e9 + 7;
const int inf = 1e9;
int add(int x, int y) {
return (1ll * x + 1ll * y) % mod;
}
int del(int x, int y) {
return ((1ll * x - 1ll * y) % mod + mod) % mod;
}
int mul(int x, int y) {
return (1ll * x * 1ll * y) % mod;
}
map<pair<int, ii>, int> mymap;
int sum1, sum2, sum3, n;
string s;
int main() {
cin.tie(0), ios_base::sync_with_stdio(0);
cin >> n;
cin >> s;
s = "+" + s;
mymap[{0, {0, 0}}] = 0;
int ans = 0;
for(int i = 1; i <= n; i++) {
if(s[i] == 'J')
sum1++;
else if(s[i] == 'O')
sum2++;
else
sum3++;
int lmao1 = sum1, lmao2 = sum2, lmao3 = sum3;
lmao1 -= min(min(sum1, sum2), sum3);
lmao2 -= min(min(sum1, sum2), sum3);
lmao3 -= min(min(sum1, sum2), sum3);
//cout << lmao1 << " " << lmao2 << " " << lmao3 << " " << mymap.count({lmao1, {lmao2, lmao3}}) << "\n";
if(mymap.count({lmao1, {lmao2, lmao3}}))
ans = max(ans, i - mymap[{lmao1, {lmao2, lmao3}}]);
if(mymap.count({lmao1, {lmao2, lmao3}}) == 0)
mymap[{lmao1, {lmao2, lmao3}}] = i;
}
cout << ans;
}
