N = input()
n = N
if n % 3 == 0:
    print 3
else:
    cnt = 0
    while n % 2 == 0:
        n /= 2
        cnt += 1
    if cnt >= 2:
        print 4
    else:
        flag = False
        for i in xrange(3, int(N**0.5)+1, 2):
            if N % i == 0:
                flag = True
                break
        if flag:
            print i
        else:
            print n