import math
N = int(input())

for i in range(2, N):
    c = 0
    if i%2==0 and i != 2:
        continue
    for divisor in range(2, math.floor(math.sqrt(i))+1):
        if i % divisor == 0:
            c = 1
            break
    if c == 0 and N % i == 0 and i != 2:
        print(i)
        break