#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>
#include <list>
using namespace std;
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
template<class T> inline T sqr(T x) { return x*x; }
typedef pair<int, int> P;
typedef long long ll;
typedef unsigned long long ull;

#define For(i,a,b)	for(int (i) = (a);i < (b);(i)++)
#define rep(i,n)	For(i,0,n)
#define clr(a)		memset((a), 0 ,sizeof(a))
#define mclr(a)		memset((a), -1 ,sizeof(a))
#define all(a)		(a).begin(),(a).end()
#define rall(a)		(a).rbegin(), (a).rend()
#define sz(a)		(sizeof(a))
#define Fill(a,v)	fill((int*)a,(int*)(a+(sz(a)/sz(*(a)))),v)

bool cheak(int x, int y, int xMax, int yMax){ return x >= 0 && y >= 0 && xMax > x && yMax > y; }
const int dx[9] = { -1, -1, -1, 0 , 0 , 0 , 1 , 1 , 1}, dy[9] = { -1, 0, 1 ,-1 , 0 , 1, -1 , 0,  1};
const int mod = 1000000007;
const int INF = 1e9;

ll c[11];
int b, n;
ll ave = 0;

ll cast(){
	int m = b;
	int ret = 0;
	rep(i, n){
		if (c[i] > ave){
			m += c[i] - ave;
			ret += c[i] - ave;
		}
	}
	rep(i, n){
		if (c[i] < ave){
			m -= ave - c[i];
			ret += ave - c[i];
		}
	}
	return ret;
}

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

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

	if (sum % n > n / 2){
		ave++;
	}
	ave += sum / n;
	ll ans = INF;
	For(i, ave - 1e6, ave + 1e6)ans = min(ans, cast());
	cout << ans << endl;

	return 0;
}