#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 );
  sort( C.begin(), C.end() );
  ll minv1 = 1LL << 62, minv2 = 1LL << 62;
  int minid1, minid2;
  for( int i = 0; i < N; ++i ){
    ll v = ok( B, C, C[ i ] );
    if( minv1 > v )
      minv1 = v,
      minid1 = i;
    else if( minv2 > v )
      minv2 = v,
      minid2 = i;
  }
  assert( abs( minid1 - minid2 ) == 1 );
  int g = C[ minid1 ];
  for( int lb = C[ minid1 ], rb = C[ minid2 ]; lb + 1 <= rb; ){
    if( lb + 1 == rb ){
      ll vl = ok( B, C, lb );
      ll vr = ok( B, C, rb );
      if( vl < vr )
        g = lb;
      else
        g = rb;
      break;
    }
    int x = lb + ( rb - lb + 2 ) / 3;
    int y = rb - ( rb - lb + 2 ) / 3;
    // cout << lb << " " << x << " " << y << " " << rb << endl;
    ll vl = ok( B, C, lb );
    ll vx = ok( B, C, x );
    ll vy = ok( B, C, y );
    ll vr = ok( B, C, rb );
    if( vl <= vx and vx <= vy and vy <= vr )
      g = rb = y;
    else if( vl >= vx and vx <= vy and vy <= vr )
      g = rb = y;
    else if( vl >= vx and vx >= vy and vy <= vr )
      g = lb = x;
    else if( vl >= vx and vx >= vy and vy >= vr )
      g = lb = x;
  }
  cout << ok( B, C, g ) << endl;
  return 0;
}