a, b, s = map(int, input().split())

ans = 0
for h in range(1, a + 1):
    if h > s:
        break
    wmin = 1
    wmax = min(b, s // h)

    R = b - wmin + 1
    L = b - wmax + 1
    n = R * (R + 1) // 2 - L * (L - 1) // 2

    ans += (a - h + 1) * n

print(ans)