var n, m, x, y, k, i, t: integer;
                      a: array[1..4] of integer;

   begin
    read(n, m, x, y);
    if m > n
     then begin
           a[1] := x;
           a[2] := n - a[1];
           a[3] := y;
           a[4] := m - a[3];
          end
     else begin
           a[1] := x;
           a[2] := m - a[1] ;
           a[3] := y;
           a[4] := n - a[3];
          end;

     for k := 1 to 3 do
      for i := 1 to 4 - k do
       if a[i] > a[i + 1]
        then begin
              t :=a [i];
              a[i] := a[i + 1];
              a[i+1] := t
             end;
    write(a[1]);
 end.