import java.io.InputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import java.math.BigInteger;

public class Main{

static PrintWriter out;
static InputReader ir;

static void solve(){
 BigInteger n=ir.nextBigInteger();
 if(n.compareTo(b(4))==0) out.println(3);
 else if(n.compareTo(b(6))==0) out.println(5);
 else if(n.compareTo(b(8))==0||n.compareTo(b(9))==0||n.compareTo(b(10))==0||n.compareTo(b(15))==0||n.compareTo(b(16))==0||n.compareTo(b(22))==0) out.println(7);
 else if(n.compareTo(b(12))==0) out.println(11);
 else if(n.compareTo(b(14))==0||n.compareTo(b(15))==0) out.println(13);
 else if(n.compareTo(b(20))==0||n.compareTo(b(21))==0) out.println(19);
 else if(n.compareTo(b(24))==0||n.compareTo(b(25))==0) out.println(23);
 else if(n.add(b(7)).remainder(b(8)).compareTo(b(0))==0&&n.subtract(b(8)).isProbablePrime(50)) out.println(14);
 else out.println(8);
}

public static BigInteger b(long n){
 return BigInteger.valueOf(n);
}

public static boolean isPrime(long n,int k){
 if(n==2) return true;
 if(n<2||(n&1)==0) return false;
 long d=(n-1)>>1;
 while((d&1)==0) d>>=1;
 for(int i=0;i<k;i++){
  long a=(long)(Math.random()*(n-1))+1;
  long t=d;
  long y=BigInteger.valueOf(a).modPow(BigInteger.valueOf(t),BigInteger.valueOf(n)).longValue();
  while(t!=n-1&&y!=1&&y!=n-1){
   y=BigInteger.valueOf(y).modPow(BigInteger.valueOf(2),BigInteger.valueOf(n)).longValue();
   t<<=1;
  }
  if(y!=n-1&&(t&1)==0) return false;
 }
 return true;
}

public static void main(String[] args) throws Exception{
 ir=new InputReader(System.in);
 out=new PrintWriter(System.out);
 solve();
 out.flush();
}

static class InputReader {
 private InputStream in;
 private byte[] buffer=new byte[1024];
 private int curbuf;
 private int lenbuf;

 public InputReader(InputStream in) {this.in=in; this.curbuf=this.lenbuf=0;}
 
 public boolean hasNextByte() {
  if(curbuf>=lenbuf){
   curbuf= 0;
   try{
    lenbuf=in.read(buffer);
   }catch(IOException e) {
    throw new InputMismatchException();
   }
   if(lenbuf<=0) return false;
  }
  return true;
 }

 private int readByte(){if(hasNextByte()) return buffer[curbuf++]; else return -1;}
 
 private boolean isSpaceChar(int c){return !(c>=33&&c<=126);}
 
 private void skip(){while(hasNextByte()&&isSpaceChar(buffer[curbuf])) curbuf++;}
 
 public boolean hasNext(){skip(); return hasNextByte();}
 
 public String next(){
  if(!hasNext()) throw new NoSuchElementException();
  StringBuilder sb=new StringBuilder();
  int b=readByte();
  while(!isSpaceChar(b)){
   sb.appendCodePoint(b);
   b=readByte();
  }
  return sb.toString();
 }
 
 public int nextInt() {
  if(!hasNext()) throw new NoSuchElementException();
  int c=readByte();
  while (isSpaceChar(c)) c=readByte();
  boolean minus=false;
  if (c=='-') {
   minus=true;
   c=readByte();
  }
  int res=0;
  do{
   if(c<'0'||c>'9') throw new InputMismatchException();
   res=res*10+c-'0';
   c=readByte();
  }while(!isSpaceChar(c));
  return (minus)?-res:res;
 }
 
 public long nextLong() {
  if(!hasNext()) throw new NoSuchElementException();
  int c=readByte();
  while (isSpaceChar(c)) c=readByte();
  boolean minus=false;
  if (c=='-') {
   minus=true;
   c=readByte();
  }
  long res = 0;
  do{
   if(c<'0'||c>'9') throw new InputMismatchException();
   res=res*10+c-'0';
   c=readByte();
  }while(!isSpaceChar(c));
  return (minus)?-res:res;
 }

 public double nextDouble(){return Double.parseDouble(next());}

 public BigInteger nextBigInteger(){return new BigInteger(next());}

 public int[] nextIntArray(int n){
  int[] a=new int[n];
  for(int i=0;i<n;i++) a[i]=nextInt();
  return a;
 }

 public long[] nextLongArray(int n){
  long[] a=new long[n];
  for(int i=0;i<n;i++) a[i]=nextLong();
  return a;
 }

 public char[][] nextCharMap(int n,int m){
  char[][] map=new char[n][m];
  for(int i=0;i<n;i++) map[i]=next().toCharArray();
  return map;
 }
}
}