C

e = []
a,b,k = map(int,input().split())
if a > b:
    for i in range(1, b+1):
        if a%i ==0 and b%i == 0:
            e.append(i)
elif a == b:
    e.append(1)
    e.append(a)
else:
    for p in range(1, a+1, 1):
        if b%p ==0 and a%p == 0:
            e.append(p)
try:
    print (e[k-1])
except IndexError:
    print (0)