#include <iostream>
#include <vector>
using namespace std;

int main() {
	int n;
	cin >> n;
	
	vector<bool> isPrime(n + 10, true);
	vector<int> primes;
	for(int i = 2; i <= n; i++){
		if(isPrime[i]) primes.push_back(i);
		
		for(int j = 0; j < primes.size() && primes[j] * i <= n; j++){
			isPrime[primes[j] * i] = false;
			if(i % primes[j] == 0) break;
		}
	}
	
	int pos = primes.size() - 1;
	while(pos >= 2 && n % primes[pos] != 0) pos--;
	cout << primes[pos];
	return 0;
}