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

typedef long long ll;

ll ok( int b, const vector< int > &c, int gol ){
  ll res = 0;
  ll x = b;
  for( int i = 0; i < c.size(); ++i )
    if( c[ i ] > gol )
      x += c[ i ] - gol,
      res += c[ i ] - gol;
  for( int i = 0; i < c.size(); ++i )
    if( c[ i ] < gol )
      x -= gol - c[ i ],
      res += gol - c[ i ];
  if( x < 0 )
    return 1LL << 62;
  return res;
}

signed main(){
  int B; cin >> B;
  int N; cin >> N;
  vector< int > C( N );
  for( int i = 0; i < N; ++i )
    cin >> C[ i ];
  if( N == 1 )
    cout << 0 << endl, exit( 0 );
  ll csum = 0;
  for( int i = 0; i < N; ++i )
    csum += C[ i ];
  int lb = 0, rb = ( csum + B ) / N + 1;
  while( rb - lb > 3 ){
    int x = ( 2LL * lb + rb ) / 3;
    int y = ( 2LL * rb + lb ) / 3;
    if( ok( B, C, x ) <= ok( B, C, y ) )
      rb = y;
    else
      lb = x;
  }
  ll ans = 1LL << 62;
  for( int i = lb; i < rb; ++i )
    ans = min( ans, ok( B, C, i ) );
  cout << ans << endl;
  return 0;
}