#include <bits/stdc++.h>
using namespace std;
const int maxN = 2e5 + 5;
const int c[3] = {'J', 'O', 'I'};
int n;
int pfs[maxN][3];
inline bool check (int x) {
x *= 3;
for (int i = x; i <= n; i ++) {
int j = i - x + 1;
vector <int> t(3, 0);
for (int k = 0; k < 3; k ++) {
t[k] += pfs[i][k] - pfs[j - 1][k];
}
if (t[0] == t[1] && t[1] == t[2]) {
return true;
}
}
return false;
}
signed main () {
ios_base :: sync_with_stdio (0);
cin.tie (0);
cin >> n;
for (int i = 1; i <= n; i ++) {
char cc;
cin >> cc;
for (int j = 0; j < 3; j ++) {
if (cc == c[j]) {
pfs[i][j] = pfs[i - 1][j] + 1;
}
else {
pfs[i][j] = pfs[i - 1][j];
}
}
}
int l = 0, r = n / 3, res = 0;
while (true) {
if (l > r) {
break;
}
int mid = (l + r) >> 1;
if (check (mid)) {
res = mid;
l = mid + 1;
}
else {
r = mid - 1;
}
}
cout << res * 3;
}
