//
//  main.cpp
//  p1787
//
//  Created by Huan Lin on 21/1/14.
//  Copyright (c) 2014 Huan Lin. All rights reserved.
//

#include <iostream>
#include <stdio.h>

using namespace std;

int main(int argc, const char * argv[])
{

    int k,n;
    cin >> k >> n;



    int jam = 0;

    for (int i = 0; i < n; i++) {
        int num;
        cin >> num;

        jam = jam + num - k;
        if (jam < 0) jam = 0;

    }

    cout << jam;
}

remove it!