import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.ArrayDeque;
import java.util.BitSet;
import java.util.HashMap;
import java.util.Queue;
 
public class Main {
	public static void main(String[] args) throws NumberFormatException,
	IOException {Solve solve = new Solve();solve.solve();}
}
class Solve{
	void solve() throws NumberFormatException, IOException{
		ContestScanner in = new ContestScanner();
		Writer out = new Writer();
//		if(exp()) return;
		BigInteger bi = new BigInteger(in.readLine());
		if(bi.compareTo(BigInteger.valueOf(40L))>=0){
			if(bi.mod(BigInteger.valueOf(8)).equals(BigInteger.valueOf(1))
					&& bi.add(BigInteger.valueOf(8)).isProbablePrime(100)) System.out.println(14);
			else System.out.println(8);
			return;
		}
		BitSet p = prime(50);
		int n = bi.intValue();
		for(int w=3; w<n; w++){
			final int h = (n+w-1)/w;
			boolean[][] map = new boolean[h][w];
			for(int i=0; i<n; i++){
				final int y = i/w;
				final int x = i%w;
				map[y][x] = p.get(i+1);
			}
			if(n%w!=0) for(int i=n%w; i<w; i++){
				map[h-1][i] = true;
			}
//			for(int i=0; i<h; i++){
//				for(int j=0; j<w; j++){
//					System.out.print(map[i][j]?'X':'.');
//				}
//				System.out.println();
//			}
//			System.out.println();
			if(check(map, n-1)){
				System.out.println(w);
				return;
			}
		}
		System.out.println(n-1);
	}
	
	boolean exp(){
		int n = 100;
		BitSet p = prime(n);
		for(int i=1; i<=n; i++){
			if(p.get(i)) System.out.print('X');
			else System.out.print('.');
			if(i%8==0) System.out.println();
		}
		return true;
	}
	
	final int[] dx = {0, 1, 0, -1};
	final int[] dy = {1, 0, -1, 0};
	boolean check(boolean[][] map, int goal){
		final int h = map.length;
		final int w = map[0].length;
		Queue<Integer> qu = new ArrayDeque<>();
		qu.add(0);
		BitSet used = new BitSet(h*w);
		while(!qu.isEmpty()){
			int p = qu.poll();
			if(used.get(p)) continue;
			used.set(p);
			if(goal==p) return true;
			final int y = p/w;
			final int x = p%w;
			for(int i=0; i<4; i++){
				final int ny = dy[i]+y;
				final int nx = dx[i]+x;
				if(ny<0||ny>=h||nx<0||nx>=w||map[ny][nx])
					continue;
				qu.add(ny*w+nx);
			}
		}
		return false;
	}
	
	public static BitSet prime(int max){
		// こちらを使うように
		BitSet prime = new BitSet(max+1);
		prime.set(2, max+1);
		for(int i=2; i!=-1 && i*i<=max; i=prime.nextSetBit(i+1))
			for(int j=i*2; j<=max; j+=i) prime.clear(j);
		return prime;
	}
}
 
class MultiSet<T> extends HashMap<T, Integer>{
	@Override
	public Integer get(Object key){return containsKey(key)?super.get(key):0;}
	public void add(T key,int v){put(key,get(key)+v);}
	public void add(T key){put(key,get(key)+1);}
}
class Timer{
	long time;
	public void set(){time = System.currentTimeMillis();}
	public long stop(){return System.currentTimeMillis()-time;}
}
class Writer extends PrintWriter{
	public Writer(String filename) throws IOException
	{super(new BufferedWriter(new FileWriter(filename)));}
	public Writer() throws IOException{super(System.out);}
}
class ContestScanner {
	private BufferedReader reader;
	private String[] line;
	private int idx;
	public ContestScanner() throws FileNotFoundException 
	{reader = new BufferedReader(new InputStreamReader(System.in));}
	public ContestScanner(String filename) throws FileNotFoundException
	{reader = new BufferedReader(new InputStreamReader(new FileInputStream(filename)));}
	public String nextToken() throws IOException {
		if (line == null || line.length <= idx) {
			line = reader.readLine().trim().split(" ");
			idx = 0;
		}
		return line[idx++];
	}
	public String readLine() throws IOException{return reader.readLine();}
	public long nextLong() throws IOException, NumberFormatException
	{return Long.parseLong(nextToken());}
	public int nextInt() throws NumberFormatException, IOException
	{return (int) nextLong();}
	public double nextDouble() throws NumberFormatException, IOException 
	{return Double.parseDouble(nextToken());}
}