12802

#include <iostream>
#include <stdio.h>
#include <vector>

using namespace std;

int prime[1000001];
vector<int> v;

int palin(int a)
{
	if(a<=11)
	return 1;

	int org=a;
	int r=0;
	while(a)
	{
		r*=10;
		r+=(a%10);
		a/=10;
	}
	if(r==org)
	return 1;

	return 0;
}
int main()
{
	for(int j=1;j<1000001;j++)
	prime[j]=0;

	for(int i=2;i<1000001/2;i++)
	{
		if(prime[i]==0)
		for(int j=i+i;j<1000001;j+=i)
		prime[j]=1;
	}

	for(int i=1;i<1000001;i++)
	{
		if(prime[i]==0)
		{
			if(palin(i))
			//cout<<i<<"\n";
				//v.push_back(i);
				prime[i]=-3;
		}

	}

	//cout<<v.size()<<"\n";
	int n;
	while(cin>>n)
	{
		cout<<2*n<<"\n";
		if(prime[n]==-3)
		break;
	}
	return 0;
}