import math

def main():
    N = int(input())

    n = int(math.sqrt(N))
    for i in range(3, n + 1):
        if not N % i:
            break
    else:
        if N % 2:
            i = N
        else:
            i = N // 2
            if i <= 2:
                i = 4

    print(i)

main()