#include <iostream>

long long f(long long N)
{
    if (N <= 5) {
        return N;
    }
    if ((N % 4) == 0) {
        return 4;
    }
    while ((N % 2) == 0) {
        N /= 2;
    }
    for (long long n = 3; n <= (N / n);) {
        if ((N % n) == 0) {
            return n;
        }
        n += 2;
        if ((N % n) == 0) {
            return n;
        }
        n += 2;
        if ((N % n) == 0) {
            return n;
        }
        n += 4;
    }
    return N;
}

int main()
{
    long long N;
    std::cin >> N;
    std::cout << f(N) << std::endl;
    return 0;
}