Китайский язык

#define _USE_MATH_DEFINES
#include <iostream>
#include <conio.h>
#include <string>
#include <set>
#include <map>
#include <algorithm>
#include <string>
#include <math.h>
#include <vector>
#include <cmath>
#include <sstream>

using namespace std;

int main()
{
    long long prom, n, people, sum=0;

    cin >> people >> n;

    for (int i = 1; i <= n; i++)
    {
        cin >> prom;
        sum += prom;
    }

    cout << max(sum - people*(n - 1), (long long)0);

    _getch();
    return 0;
}