#include<bits/stdc++.h>
using namespace std;
using Int = long long;

template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int b,n;
  cin>>b>>n;
  vector<Int> c(n);
  for(Int i=0;i<n;i++) cin>>c[i];
  Int x=b;
  for(Int i=0;i<n;i++) x+=c[i];

  Int ans=1e18;
  auto check=
    [&](Int k)->Int{
      Int res=0;
      for(Int i=0;i<n;i++) res+=abs(k-c[i]);
      chmin(ans,res);
      return res;
    };
  
  Int l=0,r=x/n;
  check(l);check(r);
  while(l+1<r){
    Int m=(l+r)>>1;
    if(check(m)<check(m+1)) r=m;
    else l=m;    
  }
  check(l);check(r);
  cout<<ans<<endl;
  return 0;
}