import std.algorithm, std.array, std.container, std.range, std.bitmanip;
import std.numeric, std.math, std.bigint, std.random, core.bitop;
import std.string, std.regex, std.conv, std.stdio, std.typecons;

void main()
{
  auto b = readln.chomp.to!long;
  auto n = readln.chomp.to!size_t;
  auto ci = iota(n).map!(_ => readln.chomp.to!long).array;

  long calc(long r) { return ci.map!(c => (c - r).abs.to!long).sum; }

  auto mi = 0L, ma = (ci.sum + b) / n, r = -1L;
  while (ma - mi > 2) {
    auto mt1 = (mi * 2 + ma) / 3;
    auto mt2 = (mi + ma * 2) / 3;
    auto r1 = calc(mt1);
    auto r2 = calc(mt2);
    if (r1 > r2) {
      mi = mt1;
    } else {
      ma = mt2;
    }
  }
  r = iota(mi, ma + 1).map!(r => calc(r)).reduce!(min);

  writeln(r);
}