#include <iostream>

using namespace std;

int main()
{
    int k;
    cin >> k;

    int n;
    cin >> n;

    int change;
    int result = 0;

    for (int i = 0; i < n; i++)
    {
        cin >> change;
        result += change;
    }

    if (result - k*n >= 0) cout << result - k*n;
    else cout << 0;
    return 0;
}

Author's behavior.
1) You should explain what problem is - WA/TLE/runtime error.
2) You should better remove/clear/add explanation to post after you solved task yourself.

Edited by author 16.08.2016 21:18