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

ans = 0
for i in range(1,a+1):
    na = i
    nb = min(b,s//i)
    if nb == 0:
        continue
    l = b-nb+1

    c = b*(b+1)//2 - l*(l-1)//2
    ans += (a-na+1)*c
print(ans)