Нужна идея алгоритма! Ход конём

const
    step:array [1..2,1..2] of byte=((2,1),(1,2));
var
    n,m,tempx,i,j,tempy:SMALLINT;
    head,tail:word;
    inkerx,inkery:shortint;
    queue:array [1..300000,1..2] of longword;
    chessboard:array [-2..53,-2..53] of longint;
    f,g:text;
begin
  assign(f,'knight.in'); reset(f);
  assign(g,'knight.out'); rewrite(g);
  fillchar(chessboard,sizeof(chessboard),0);
  readln(f,n,m);
  head:=1;
  tail:=2;
  queue[1,1]:=1;
  queue[1,2]:=1;
  for inkerx:=-2 to 53 do
  begin
    for inkery:=-2 to 0 do
      chessboard[inkery,inkerx]:=-1;
    for inkery:=51 to 53 do
      chessboard[inkery,inkerx]:=-1;
  end;
 
  for inkerx:=-2 to 0 do
    for inkery:=-2 to 53 do
      chessboard[inkery,inkerx]:=-1;
  for inkerx:=51 to 53 do
    for inkery:=-2 to 53 do
      chessboard[inkery,inkerx]:=-1;
  chessboard[1,1]:=1;
  queue[1,1]:=1;
  queue[1,2]:=1;
  head:=1;
  tail:=2;
  while head<tail do
  begin
    tempx:=queue[head,1];
    tempy:=queue[head,2];
    inc(head);
    for i:=1 to 2 do
     begin
       if (chessboard[tempx+step[i,1],tempy+step[i,2]]<>-1) and ((tempx+step[i,1]<=n) and (tempy+step[i,2]<=m))
       then begin
       chessboard[tempx+step[i,1],tempy+step[i,2]]:=chessboard[tempx+step[i,1],tempy+step[i,2]]+1;
       queue[tail,1]:=tempx+step[i,1];
       queue[tail,2]:=tempy+step[i,2];
       inc(tail);
       end;
     end;
  end;
  writeln(g,chessboard[n,m]);
  close(f);
  close(g);
end.