#include <bits/stdc++.h>
#define PB push_back
#define MP make_pair
#define REP(i,n) for (int i=0;i<(n);i++)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define ALL(a) (a).begin(),(a).end()
int INF=1e9;
int MOD=1000000007;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
double EPS = 1e-10;
ull pow1(ull base,ull power,ull mod){
	ull result=1;
	while(power>0){
		if(power&1==1)result=(result*base)%mod;
		base=(base*base)%mod;
		power>>=1;
	}
	return result;
}
bool is_prime(ull n){
	if(n==2)return true;
	if(n==1||n&1==0)return false;
	ull d=n-1;
	while(d&1==0)d>>=1;
	REP(i,1000){
		ull a=rand()%(n-2)+1;
		ull t=d;
		ull y=pow1(a,t,n);
		while(t!=n-1&&y!=1&&y!=n-1){
			y=(y*y)%n;
			y<<=1;
		}
		if(y!=n-1&&y&1==0)return false;
	}
	return true;
}
int main(){
	srand((unsigned)time(NULL));
	ull s;
	cin>>s;
	if(s==1){
		cout<<1<<endl;
		return 0;
	}
	if(s==4){
		cout<<3<<endl;
		return 0;
	}
	if(s==6){
		cout<<5<<endl;
		return 0;
	}
	if(s==8||s==9||s==10||s==15||s==16||s==22){
		cout<<7<<endl;
		return 0;
	}
	if(s==12){
		cout<<11<<endl;
		return 0;
	}
	if(s==14||s==15||s==16){
		cout<<13<<endl;
		return 0;
	}
	if(s==20||s==21||s==22){
		cout<<19<<endl;
		return 0;
	}
	if(s==24||s==25){
		cout<<23<<endl;
		return 0;
	}
	if(s%(ll)8!=1)cout<<8<<endl;
	else if(!is_prime(s-(ll)8))cout<<8<<endl;
	else cout<<14<<endl;
	return 0;
}