#include <iostream>
#include <cmath>
#include <algorithm>

#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define ll long long
using namespace std;

int b, n, *c;

ll solve(ll k)
{
	ll res = 0, rest = b;

	rep(i,0,n) {
		rest += c[i] - k;
		res += abs(c[i] - k);
	}

	return res;
}

int main(void)
{
	cin >> b >> n;

	c = new int[n];
	ll sum = b;
	rep(i, 0, n) {
		cin >> c[i];
		sum += c[i];
	}

	ll A, B, C1, C2, T1, T2, res, tmp;
	A = 0;
	B = sum / n;
	while(A < B-10) {
		C1 = (A+A+B) / 3;
		C2 = (A+B+B) / 3;
		T1 = solve(C1);
		T2 = solve(C2);
		if(T1 > T2) A = C1;
		else B = C2;
	}

	res = 1000000000000000LL;
	for(ll i=A;i<=B;i++) {
		tmp = solve(i);
		res = min(res, tmp);
	}

	cout << res << endl;

	return 0;
}