H, W, N = [int(s) for s in input().split()]
imos = [[0] * (W + 1) for _ in range(H + 1)]

for _ in range(N):
    r1, c1, r2, c2 = [int(s) - 1 for s in input().split()]
    imos[r1][c1] += 1
    imos[r2 + 1][c1] -= 1
    imos[r1][c2 + 1] -= 1
    imos[r2 + 1][c2 + 1] += 1

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

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

not_exists = sum(sum(v >= 1 for v in row) for row in imos)
print(H * W - not_exists)