#prepare
L = []
Q = []

#input
W, H, N, = map(int,raw_input().split())
for i in range(N):
    L.append(map(int,raw_input().split()))
x1=0
x2=W
y1=0
y2=H

#calculate
Q = [row[2] for row in L]


for k in range(N):
    if Q[k] == 1:
        x1 = max(x1,L[k][0])
    elif Q[k] == 2:
        x2 = min(x2,L[k][0])
    elif Q[k] == 3:
        y1 = max(y1,L[k][1])
    elif Q[k] == 4:
        y2 = min(y2,L[k][1])

print(max(0,x2-x1) * max(0,y2-y1)0