Free spots

Write a program, that, given a board, and a list of rectangular sub-portions of the board, returns the number of positions that belong to no sub-portion. Input The input consists of a series of test sets separated by blank lines. A test set starts with a line with three numbers W, H and N, giving respectively the width, the height and the number of sub-boards. These values satisfy the following constraints: 1 ≤ W,H ≤ 500 and 0 ≤ N ≤ 99. Follow then N lines, composed of four integers X1, Y1, X2, Y2, such that (X1, Y1) and (X2, Y2) are the positions of two opposite corners of a sub-board. These values satisfy the following constraints: 1 ≤ X1,X2 ≤ W and 1 ≤ Y1,Y2 ≤ H. The end of the input is reached when the numbers W, H and N are equal to 0. This last line shall not be considered as a test set. Output The program shall output each result on a line by its own, following the format given in the sample output. Sample Input 111 1111 222 1112 1121 493 182 3 349 148 363 146 241 123 443 147 303 124 293 17 000 Sample Output There is no empty spots. There is one empty spot. There are 83470 empty spots.