a, b, s = map(int, input().split())
ans = 0
for h in range(1, a + 1):
    if h > s:
        break
    w = min(s // h, b)
    hh = a - h + 1
    mi_w = b - w + 1
    ma_w = b
    ww = (mi_w + ma_w) * (ma_w - mi_w + 1) // 2
    ans += hh * ww
print(ans)