#include <bits/stdc++.h>
using namespace std;
#define ll long long
int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
#ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
#endif
    int n;
    cin >> n;
    string s;
    cin >> s;
    int ans = 0;
    vector<int> idx;
    char a = s.front();
    char b = s.back();
    if (a == b) {
        cout << n - 1 << '\n';
        return 0;
    }
    for (int i = n - 1; i >= 0; --i) {
        if (s[i] == b) idx.push_back(i);
    }
    for (int i = 0; i < n; ++i) {
        while (idx.size() && idx.back() <= i) idx.pop_back();
        if (s[i] == a && idx.size()) {
            ans = max(ans, i + (n - idx.back() - 1));
        }
    }
    cout << ans << '\n';
    return 0;
}