import std.stdio, std.conv, std.math, std.string, std.range, std.array,
       std.algorithm;

void main() {
  auto buf = readln().strip().split().map!(to!int)().array();
  immutable N = buf[0];
  immutable M = buf[1];

  int[] D = new int[](M);

  foreach(immutable int i; 0 .. M) {
    D[i] = readln().strip().to!int();
  }

  D.sort();

  int[] p;
  int[] n;

  n ~= 0;
  p ~= 0;

  foreach(d; D) {
      if(d < 0) {
          n ~= d;
      } else {
          p ~= d;
      }
  }
  n.sort!"a>b"();
  
  int ans = int.max;

  foreach(i; 0..N+1) {
      if(p.length <= i) {
          break;
      }
      int j = N - i;
      if(n.length <= j) {
          continue;
      }
      //writeln(i, ", ", j);
      immutable tdisr =  p[i] + p[i]-n[j];
      immutable tdisl = -n[j] + p[i]-n[j];
      //tdisr.writeln;
      //tdisl.writeln;
      ans = min(ans, tdisr, tdisl);
  }

  ans.writeln;
}