# 座標圧縮解法
H, W, N = map(int, input().split())

R = [0, H]
C = [0, W]

queries = []
for _ in range(N):
    r1, c1, r2, c2 = map(int, input().split())
    r1 -= 1
    c1 -= 1
    queries.append((r1, c1, r2, c2))
    R.append(r1)
    R.append(r2)
    C.append(c1)
    C.append(c2)

R = sorted(list(set(R)))
C = sorted(list(set(C)))

R_map = {v: i for i, v in enumerate(R)}
C_map = {v: i for i, v in enumerate(C)}

h = len(R)
w = len(C)

grid = [[0] * w for _ in range(h)]

for r1, c1, r2, c2 in queries:
    grid[R_map[r1]][C_map[c1]] += 1
    grid[R_map[r1]][C_map[c2]] -= 1
    grid[R_map[r2]][C_map[c1]] -= 1
    grid[R_map[r2]][C_map[c2]] += 1

for i in range(h):
    for j in range(1, w):
        grid[i][j] += grid[i][j-1]

for j in range(w):
    for i in range(1, h):
        grid[i][j] += grid[i-1][j]

ans = 0
for i in range(h - 1):
    for j in range(w - 1):
        if grid[i][j] == 0:
            ans += (R[i+1] - R[i]) * (C[j+1] - C[j])

print(ans)