#include <iostream>
#include <fstream>

using namespace std;

ifstream reader("DATA2.txt");
ofstream writer("OUT2.txt");

int primes[] = {2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103};

int main(){
    int m;
    while(reader >> m){
        int a = 0;
        for(a = 0; primes[a] < m; ++a){
            // do nothing
        }
        if(m == primes[a]){
            if((primes[a+2] - m) <= (m - primes[a-2]))
                writer << primes[a+2] << endl;
            else
                writer << primes[a-2] << endl;
        }else{
            if((primes[a+1] - m) <= (m - primes[a-2]))
                writer << primes[a+1] << endl;
            else
                writer << primes[a-2] << endl; 
        }
    }
    return 0;
}