b = int(input())
a = []
c = []
for i in range(1,b+1):
    if b % i == 0:
        a.append(i)


for i in a[1:]:
    for j in range(2,i):
        if i % j ==0:
            break
    else:
        c.append(i)
c.sort()
print(c[-1])