import java.math.BigInteger;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Scanner;
import java.util.Set;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		BigInteger N = new BigInteger(sc.next());
		
		final BigInteger four = BigInteger.valueOf(4);
		final BigInteger six = BigInteger.valueOf(6);
		final BigInteger eight = BigInteger.valueOf(8);
		final BigInteger nine = BigInteger.valueOf(9);
		final BigInteger ten = BigInteger.valueOf(10);
		final BigInteger twelve = BigInteger.valueOf(12);
		final BigInteger fourteen = BigInteger.valueOf(14);
		final BigInteger fifteen = BigInteger.valueOf(15);
		final BigInteger sixteen = BigInteger.valueOf(16);
		final BigInteger eighteen = BigInteger.valueOf(18);
		final BigInteger twenty = BigInteger.valueOf(20);
		final BigInteger twentyone = BigInteger.valueOf(21);
		final BigInteger twentytwo = BigInteger.valueOf(22);
		final BigInteger twentyfour = BigInteger.valueOf(24);
		final BigInteger twentyfive = BigInteger.valueOf(25);
		
		if(N.equals(four)){
			System.out.println(3);
		}else if(N.equals(six)){
			System.out.println(5);
		}else if(N.equals(eight) || N.equals(nine) || N.equals(ten) || N.equals(fifteen) || N.equals(sixteen) || N.equals(twentytwo)){
			System.out.println(7);
		}else if(N.equals(twelve)){
			System.out.println(11);
		}else if(N.equals(fourteen)){
			System.out.println(13);
		}else if(N.equals(eighteen)){
			System.out.println(17);
		}else if(N.equals(twenty) || N.equals(twentyone)){
			System.out.println(19);
		}else if(N.equals(twentyfour) || N.equals(twentyfive)){
			System.out.println(23);
		}else if(N.subtract(BigInteger.ONE).mod(eight).equals(BigInteger.ZERO)){
			System.out.println(N.subtract(BigInteger.ONE).subtract(BigInteger.ONE));
		}else{
			System.out.println(8);
		}
		
	}

}