import java.util.*;
import java.math.*;
class Main{
	static int small[]={0,0,0,0,3,0,5,0,7,7,7,0,11,0,13,7,7,0,8,0,19,19,7,0,23,23};
	public static void main(String[] args){
		Scanner s=new Scanner(System.in);
		BigInteger bi=s.nextBigInteger();
		if(bi.compareTo(new BigInteger("26"))==-1){
			System.out.println(small[bi.intValue()]);
			System.exit(0);
		}
		if(bi.mod(new BigInteger("8")).equals(BigInteger.ONE)&&bi.subtract(new BigInteger("8")).isProbablePrime(100)){
			if(bi.mod(new BigInteger("14")).equals(BigInteger.ONE)&&bi.subtract(new BigInteger("14")).isProbablePrime(100)){
				System.out.println(17);
			}else{
				System.out.println(14);
			}
		}else{
			System.out.println(8);
		}
	}
}