from sys import stdin
input = stdin.readline

INF = 1<<60

H, W, N = map(int, input().split())
AB = [list(map(int, input().split())) for _ in range(N)]

dp = [[-1]*W for _ in range(H)]
for A, B in AB:
    dp[A-1][B-1] = 0
for i in range(H):
    for j in range(W):
        if dp[i][j] == 0: continue
        if i == 0:
            dp[i][j] = 1
        else:
            dp[i][j] = dp[i-1][j]+1

ans = 0
for i in range(H):
    R = []
    stack = [(-INF, W)]
    SUM = 0
    for j in reversed(range(W)):
        while dp[i][j] <= stack[-1][0]:
            n, r = stack.pop()
            r2 = stack[-1][1]
            SUM -= (n-dp[i][j])*(r2-r)
        R.append(stack[-1][1])
        stack.append((dp[i][j], j))
        SUM += dp[i][j]
        ans += SUM
    R = R[::-1]

print(ans)