#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll B,N,A[10];
ll getLim(){
    ll ret=B;
    for(int i=0;i<N;i++)ret+=A[i];
    return ret;
}
ll ll_abs(ll val){
    return val>0?val:val*-1;
}
int main(){
    scanf("%lld%lld",&B,&N);
    for(int i=0;i<N;i++)scanf("%lld",&A[i]);

    ll lim=getLim();
    sort(A,A+N);

    ll to;
    if(A[(N-1)/2]>lim)to=lim;
    else to=A[(N-1)/2];

    ll ans=0;
    for(int i=0;i<N;i++){
        ans+=ll_abs(A[i]-to);
    }

    printf("%lld\n",ans);
    return 0;
}