H,W,N=map(int,input().split())
imos=[[0]*(W+1) for i in range(H+1)]
for i in range(N):
    r,c,R,C=map(int,input().split())
    r-=1
    c-=1
    R-=1
    C-=1
    imos[r][c]+=1
    imos[r][C+1]-=1
    imos[R+1][c]-=1
    imos[R+1][C+1]+=1

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

ans=0
for i in range(H):
    for j in range(W):
        if imos[i][j]==0:
            ans+=1
print(ans)