TOI13: Timer Switch

#include <bits/stdc++.h>

using namespace std;

using lli = long long;
const lli INF = 2e18;
const lli PB = 98765431;

int main(){

    int n;
    scanf("%d", &n);

    string str;
    cin >> str;

    lli rem = 1, hsh = 0;
    for(int i = 0; i < n; i ++){
        if(i != 0) rem = rem * PB;
        str[i] -= '0';
        hsh = hsh * PB + str[i];
    }

    lli cmp = hsh;

    for(int i = 0; i < n; i ++){
        hsh = hsh - (rem * str[i]);
        hsh = hsh * PB + str[i];
        if(hsh == cmp){
            printf("%d", i + 1);
            return 0;
        }
    }

}