prefix = [[0] * (n + 1) for _ in range(m + 1)]
suffix = [[0] * (n + 1) for _ in range(m + 1)]
for i in range(1, m + 1):
for j in range(1, n + 1):
prefix[i][j] = prefix[i - 1][j - 1] + 1
for i in range(m - 1, -1, -1):
for j in range(n - 1, -1, -1):
suffix[i][j] = suffix[i + 1][j + 1] + 1
for i in range(1, m + 1):
for j in range(1, n + 1):
ans += (prefix[i - 1][j - 1] + 1) * (suffix[i][j] + 1)