龟速乘

#include <bits/stdc++.h>
using namespace std;
int main(){
    int n;
    long long c,sum = 0;
    cin>>n>>c;
    long long a[n];
    for(int i = 0 ; i < n ; i++){
        cin>>a[i];
        a[i] %= c;
    }
    for(int i = 1 ; i < n ; i++){
        while(a[i] > 0){
            if(a[i] & 1){
                sum = (sum % c + a[0] % c) % c;
            }
            a[0] = (a[0] % c + a[0] % c) % c;
            a[i] = a[i] / 2;
        }
        a[0] = sum;
        sum = 0;
    }
    cout<<a[0]<<endl;
    return 0;
}