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 int simulate(final int N){
		boolean[] is_prime = new boolean[N + 1];
		Arrays.fill(is_prime, 2, N + 1, true);
		
		for(int i = 2; i * i <= N; i++){
			if(!is_prime[i]){ continue; }
			
			for(int j = i * 2; j <= N; j += i){
				is_prime[j] = false;
			}
		}
		
		if(is_prime[N]){ return -1; }

		boolean[] visited = new boolean[N];
		for(int mid = 1; mid <= N; mid++){
			Arrays.fill(visited, false);

			
			LinkedList<Integer> queue = new LinkedList<Integer>();
			queue.add(0);
			visited[0] = true;
			while(!queue.isEmpty()){
				final int pos = queue.poll();
				final int number = pos + 1;
				
				if(number == N){ break; }
				//System.out.println(mid + " => " + pos + " : " + (pos % mid));
				
				if(pos % mid > 0 && !is_prime[number - 1] && !visited[pos - 1]){
					queue.add(pos - 1);
					visited[pos - 1] = true;
				}
				if(pos % mid < (mid - 1) && !is_prime[number + 1] && !visited[pos + 1]){
					queue.add(pos + 1);
					visited[pos + 1] = true;
				}
				if((pos - mid) > 0 && !is_prime[number - mid] && !visited[pos - mid]){
					queue.add(pos - mid);
					visited[pos - mid] = true;
				}
				if((pos + mid) < N && !is_prime[number + mid] && !visited[pos + mid]){
					queue.add(pos + mid);
					visited[pos + mid] = true;
				}
			}
			
			if(visited[N - 1]){
				return mid;
			}
		}
		
		return -1;
	}
	
	public static int smart(final BigInteger N){
		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 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)){
			return 3;
		}else if(N.equals(six)){
			return 5;
		}else if(N.equals(eight) || N.equals(nine) || N.equals(ten) || N.equals(fifteen) || N.equals(sixteen) || N.equals(twentytwo)){
			return 7;
		}else if(N.equals(twelve)){
			return 11;
		}else if(N.equals(fourteen)){
			return 13;
		}else if(N.equals(twenty) || N.equals(twentyone)){
			return 19;
		}else if(N.equals(twentyfour) || N.equals(twentyfive)){
			return 23;
		}else if(N.subtract(BigInteger.ONE).mod(eight).equals(BigInteger.ZERO) && N.subtract(eight).isProbablePrime(1000000000)){
			return 14;
		}else{
			return 8;
		}
	}
	
	// シュミレーションして法則性を掴むべき. 
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		/*
		for(int i = 2; i <= 10000; i++){
			final int sim_value = simulate(i);
			if(sim_value > 0){
				final int big_value = smart(BigInteger.valueOf(i));
				if(sim_value != big_value){
					System.out.printf("%05d : %d, %d\n", i, sim_value, big_value);
				}
			}
		}
		*/
		
		BigInteger N = new BigInteger(sc.next());
		
		System.out.println(smart(N));
		
	}

}