import sys
input = sys.stdin.readline

H,W,N=list(map(int,input().split()))

ANS=[[0]*(W+2) for i in range(H+2)]

for i in range(N):
    x,y,z,w=list(map(int,input().split()))
    ANS[x][y]+=1
    ANS[x][w+1]-=1
    ANS[z+1][y]-=1
    ANS[z+1][w+1]+=1

for i in range(1,H+2):
    for j in range(W+2):
        ANS[i][j]+=ANS[i-1][j]


for i in range(H+2):
    for j in range(1,W+2):
        ANS[i][j]+=ANS[i][j-1]

score=0
for i in range(1,H+1):
    for j in range(1,W+1):
        if ANS[i][j]==0:
            score+=1

print(score)