import math


def main():
    n = int(input())
    ans = n
    for i in range(3, int(math.sqrt(n)) + 1):
        if n % i == 0:
            ans = i
            break

    print(ans // 2 if n % 2 == 0 and n > 4 else ans)

if __name__ == '__main__':
    main()