#import pdb; pdb.set_trace()
import sys
import math

def main():
    
    w = int(raw_input())
    h = int(raw_input())
    n = int(raw_input())
    
    ss = {}
    ks = {}
    
    for i in range(n):
        (s, k) = map(int, raw_input().split())
        
        ss[s] = 0
        ks[k] = 0
    
    print w * len(ks.keys()) + h * len(ss.keys()) - len(ks.keys()) * len(ss.keys()) - n
    
if __name__ == '__main__':
    main()