package no308;

import java.math.BigInteger;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Queue;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long n = sc.nextLong();
		if (n < 60) {
			System.out.println(solveNaive((int) n));
			return;
		}
		if (n % 8 != 1 || !BigInteger.valueOf(n-8).isProbablePrime(20)) {
			System.out.println(8);
		}else{
			System.out.println(14);
		}
	}

	public static int solveNaive(int n) {
		boolean[] isPrime = isPrimeArray(n);
		for(int w=1;w<=n;w++) {
			boolean[] used = new boolean[n+1];
			Queue<Integer> q = new ArrayDeque<>();
			used[1] = true;
			q.offer(1);
			while(!q.isEmpty()) {
				int x = q.poll();
				check(x+1,n,isPrime,used,q);
				check(x-1,n,isPrime,used,q);
				check(x+w,n,isPrime,used,q);
				check(x-w,n,isPrime,used,q);
			}
			if (used[n]) {
				return w;
			}
		}
		return -1;
	}

	public static void check(int x,int n,boolean[] isPrime,boolean[] used,Queue<Integer> q) {
		if (x < 1 || x > n || isPrime[x] || used[x]) {
			return;
		}
		used[x] = true;
		q.offer(x);
	}

	public static boolean[] isPrimeArray(int max) {
		boolean[] isPrime = new boolean[max+1];
		Arrays.fill(isPrime, true);
		isPrime[0] = isPrime[1] = false;
		for(int i=2;i*i<=max;i++) {
			if (isPrime[i]) {
				int j = i * 2;
				while(j<=max) {
					isPrime[j] = false;
					j += i;
				}
			}
		}
		return isPrime;
	}

}