#include <iostream>

using namespace std;

int main() {
    int mashines, minutes;
    cin >> mashines >> minutes;

    int arr[minutes];

    for(int i = 0; i < minutes; ++i) {cin >> arr[i];}

    int m = 0;
    for(int i = 0; i < minutes; ++i) {
        m += arr[i];

        if(m - mashines >= 0) {m -= mashines;}
        else {m = 0;}
    }

    cout << m;
}