Mina

var
  x,y,z,x1,x2,y1,y2:integer;
begin
   readln(x1,y1,x2,y2);
   x:=abs(x1-x2);
   y:=abs(y1-y2);
   while(y>0)do
    begin
     z:=x mod y;
     x:=y;
     y:=z;
    end;
   write(x+1);
end.