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

int main()
{
	int num = 0,res = 0;
	cin >> num;
	for(int i = (num - 1);i >= sqrt(num);i--)
	{
		if(num % i == 0)
		{
			for(int g = 2;g <= sqrt(i);g++)
			{
				if(i % g == 0)
				{
					res = 1;
					break;
				}
			}
			if(res == 0)
			{
				cout << i; 
				break;
			}
		}
	}
	return 0;
}