#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cctype>
#include<cstdlib>
#include<algorithm>
#include<bitset>
#include<vector>
#include<list>
#include<deque>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cmath>
#include<sstream>
#include<fstream>
#include<iomanip>
#include<ctime>
#include<complex>
#include<functional>
#include<climits>
#include<cassert>
#include<iterator>
#include<valarray>
//#include<bits/stdc++.h>
using namespace std;
#define MOD 1000000007
namespace math{
	long long int __gcd(long long int a, long long int b){
		if (a > b){
			swap(a, b);
		}
		while (a){
			swap(a, b);
			a %= b;
		}
		return b;
	}
	long long int lcm(long long int a, long long int b){
		long long int g = __gcd(a, b);
		a /= g;
		return a*b;
	}
	long long int ppow(long long int i, long long int j){
		long long int res = 1LL;
		while (j){
			if (j & 1LL){
				res *= i;
				res %= MOD;
			}
			i *= i;
			i %= MOD;
			j >>= 1LL;
		}
		return res;
	}
	namespace factorial{
		vector<long long int> lo;
		vector<double> l2;
		void set_long(long long int b){
			if (lo.size()){
			}
			else{
				lo.push_back(1);
			}
			for (long long int i = lo.size(); i <= b; i++){
				lo.push_back(lo.back());
				lo.back() *= i;
				if (lo.back() >= MOD){
					lo.back() %= MOD;
				}
			}
		}
		void set_log(long long int b){
			if (l2.size()){
			}
			else{
				l2.push_back(log(0.0));
			}
			for (long long int i = l2.size(); i <= b; i++){
				l2.push_back(l2.back());
				l2.back() += log((double)(i));
			}
		}
		long long int get_long(int b){
			if (lo.size() <= b){
				set_long(b);
			}
			return lo[b];
		}
		double get_log(int b){
			if (l2.size() <= b){
				set_log(b);
			}
			return l2[b];
		}
	}
	namespace combination{
		long long int simpleC(long long int a, long long int b){
			if (a < b){
				return 0;
			}
			if (a - b < b){
				b = a - b;
			}
			long long int u = 1LL;
			for (long long int j = a; j >= a - b + 1LL; j--){
				u *= j;
				if (u >= MOD){
					u %= MOD;
				}
			}
			long long int s = 1LL;
			for (long long int i = 1LL; i <= b; i++){
				s *= i;
				if (s >= MOD){
					s %= MOD;
				}
			}
			return (u*ppow(s, MOD - 2)) % MOD;
		}
		long long int C(long long int a, long long int b){
			if (a < b){
				return 0;
			}
			long long int u = math::factorial::get_long(a);
			long long int s = math::factorial::get_long(b)*math::factorial::get_long(a - b);
			u %= MOD;
			s %= MOD;
			return (u*ppow(s, MOD - 2)) % MOD;
		}
		double logC(int a, int b){
			double u = math::factorial::get_log(a);
			double s = math::factorial::get_log(b) + math::factorial::get_log(a - b);
			return u - s;
		}
		long long int H(long long int a, long long int b){
			return math::combination::C(a + b - 1LL, b);
		}
		long long int simpleH(long long int a, long long int b){
			return math::combination::simpleC(a + b - 1LL, b);
		}
	}
	namespace prime{
		vector<long long int> prime;
		vector<long long int> use;  //smallest divisor
		void init(int b){
			use.assign(b + 1, 0);
			prime.clear();
			prime.push_back(2);
			use[2] = 2;
			for (int i = 3; i < use.size(); i += 2){
				if (use[i] == 0LL){
					prime.push_back(i);
					use[i] = i;
					for (int j = i * 2; j < use.size(); j += i){
						use[j] = i;
					}
				}
			}
		}
		vector<int> factorizetion(long long int num){
			vector<int> r;
			r.clear();
			for (int i = 0; i<prime.size() && prime[i] * prime[i] <= num; i++){
				while (num%prime[i] == 0LL){
					r.push_back(prime[i]);
					num /= prime[i];
				}
			}
			if (num > 1LL){
				r.push_back(num);
			}
			return r;
		}
		int size_of_factorization(long long int num){
			int cnt = 0;
			for (int i = 0; i<prime.size() && prime[i] * prime[i] <= num; i++){
				while (num%prime[i] == 0LL){
					cnt++;
					num /= prime[i];
				}
			}
			if (num > 1LL){
				cnt++;
			}
			return cnt;
		}
		long long int number_of_div(long long int num){
			long long int way = 1LL;
			long long int cnt = 0;
			for (int i = 0; i < prime.size() && prime[i] * prime[i] <= num; i++){
				cnt = 0;
				while (num%prime[i] == 0){
					cnt++;
					num /= prime[i];
				}
				way *= (cnt + 1LL);
			}
			if (num > 1LL){
				way *= 2LL;
			}
			return way;
		}
	}
}

using namespace math;

long long int b;
int n;
unsigned int randxor()
{
	static unsigned int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
	unsigned int t;
	t = (x ^ (x << 11)); x = y; y = z; z = w; return(w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}
vector<long long int> v;
long long int countt(long long int a){
	long long int r = 0;
	for (int i = 0; i < v.size(); i++){
		r += abs(v[i]- a);
	}
	return r;
}
int main(){
	scanf("%lld", &b);
	scanf("%d", &n);
	long long int mint = 0;
	long long int maxt = 0;
	for (int i = 0; i < n; i++){
		long long int a;
		scanf("%lld", &a);
		v.push_back(a);
		maxt += a;
	}
	mint = countt(maxt / n);
	maxt += b;
	maxt /= (long long int)(n);
	mint = min(mint,countt(maxt));
	while (clock() / (double)(CLOCKS_PER_SEC) < 0.95){
		mint = min(mint, countt(randxor() % (maxt+1LL)));
	}
	printf("%lld\n", mint);
	return 0;
}