#include "stdafx.h"
#include <iostream>
#include <fstream>
//#include <cmath>
//#include <iomanip>
using namespace std;

bool simple (int n)
{
    int cnt = 0;
    for (int i = 2; i * i <= n; i++ )
            if (n % i == 0) cnt++;

    if (cnt == 0) return true;
        else return false;
}
int main()
{

ifstream in("input.txt");
ofstream out("output.txt");
 int a, b, cnt, ch1, ch2;
 in >> a;
 ch1 = 1;
 ch2 = 1;

 if (simple (a) == true)
     out << a;
 else
 {
    for (int i = a + 1; simple(i) != true; i++)
        ch2++;
    for (int i = a - 1; simple(i) != true; i--)
        ch1++;

    if (ch1 <= ch2) out << a - ch1;
    else out << a + ch2;

 }

     in.close();
     out.close();
    return 0;
}