program prison;
var
  p,q,i,ans,t,j,k:longint;
  sz:array[0..1001]of boolean;
  s:array[1..100]of longint;
  s2:array[1..100]of longint;
  hx:array[1..100]of boolean;
procedure find(c:longint);
var
  i:longint;
begin
  if c>q then begin
    t:=0;
    fillchar(sz,sizeof(sz),true);
    for j:=1 to q do
    begin
      k:=s2[j]-1;
      while (k>=1)and(sz[k]) do
      begin
        k:=k-1;
        t:=t+1;
      end;
      k:=s2[j]+1;
      while (k<=p)and(sz[k]) do
      begin
        k:=k+1;
        t:=t+1;
      end;
      sz[s2[j]]:=false;
    end;
    if t<ans then ans:=t;
  end
  else begin
    for i:=1 to q do
      if hx[i] then begin
        hx[i]:=false;
        s2[c]:=s[i];
        find(c+1);
        hx[i]:=true;
      end;
  end;
end;
begin
  assign(input,'prison.in');
  assign(output,'prison.out');
  reset(input);
  rewrite(output);
  readln(p,q);
  for i:=1 to q do
  begin
    read(s[i]);
  end;
  fillchar(sz,sizeof(sz),true);
  ans:=2000000000;
  t:=0;
  fillchar(hx,sizeof(hx),true);
  find(1);
  writeln(ans);
  close(input);
  close(output);
end.