a,b,s = map(int,input().split())
n = s
d = [[1] for _ in range(n+1)]
for i in range(2,n+1):
	for j in range(i,n+1,i):
		d[j].append(i)
ans = 0
for i in range(1,s+1):
	v = d[i]
	for j in range(len(v)//2):
		x,y = v[j],v[-j-1]
		ans += max(0,a-x+1)*max(0,b-y+1)
		x,y = y,x
		ans += max(0,a-x+1)*max(0,b-y+1)
	if len(v)%2==1:
		x = v[len(v)//2]
		ans += max(0,a-x+1)*max(0,b-x+1)
print(ans)