#include <iostream>
#include <math.h>
#include <vector>
#include <array>
#include <algorithm>
#include <queue>
#include <numeric>
#include <map>
#include <set>

using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) //printf(__VA_ARGS__)

typedef pair<int, int> pos;
int pos::*x = &pos::first;
int pos::*y = &pos::second;

int dxy[] = {0, 1, 0, -1, 0};

/*================================*/

signed main()
{
    int B, N;
    int C[10];
    cin >> B >> N;
    REP(i,N) cin >> C[i];

    // キャンディー全部でいくつか
    int total = B;
    int maxnum = 0;
    int minnum = pow(10, 11);
    REP(i,N) {
        total += C[i];
        maxnum = max(maxnum, C[i]);
        minnum = min(minnum, C[i]);
    }
    // 一個あたりに入れられる最大数
    maxnum = min(maxnum, total / N);
    minnum = min(minnum, maxnum);

    // 入ってる数の平均
    int ave = (total - B + N - 1) / N;
    int minc = pow(10, 11);
    int c = max(ave, maxnum);
    int k = 0;
    while (true) {
        out("check %lld\n", c);
        // 全部c個にするには何回作業が必要かカウント
        int cnt = 0;
        REP(i,N) cnt += abs(maxnum - C[i]);
        minc = min(minc, cnt);
        if (--c < 0) break;
        if (++k > 2) break;
    }

    cout << minc << endl;

    return 0;
}