#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f;
const int N = 1e6 + 10;
int a , b , c , p;
int e [N];
int main()
{
		cin >> a >> b;
		for (int i = 1; i <= b; i++)
		{
			cin >> e [i];
			p += e [i];
		}
		c = fabs (a - p);
		cout << c;
		return 0;
}