ARTIST

program hudozhik;

var
  i, w, h, a, n, S, b, x1, x2, y1, y2: integer;
  holst: array [,] of integer;

begin
  Readln(h, w);
  holst := new integer[w, h];
  Readln(n);
  for a := 0 to w - 1 do
    for b := 0 to h - 1 do
      holst[a, b] := 1;
  for i := 1 to n do
  begin
    Readln(x1, y1, x2, y2);
    for a := x1 to x2 - 1 do
      for b := y1 to y2 - 1 do
        holst[a, b] := 0;
  end;
  for a := 0 to w - 1 do
    for b := 0 to h - 1 do
      S := S + holst[a, b];
  Writeln(S);
end.