#include <bits/stdc++.h>
using namespace std;
bool prime(int a)
{
for (int i = 2;i < a;i++)
{
if (a % i == 0) return false;
}
return true;
}
int main()
{
int a, num;
cin >> a;
for (int i = a - 1;i > 0;i--)
{
if (prime(i) == true){
num = i;
break;
}
}
cout << num << endl;
return 0;