Go: package main

import "fmt"

func main() {
	var i int64
	var list = []int64{13, 19, 109, 199, 829, 1489, 1879, 2089, 3259, 3469, 5659, 9439, 13009, 15649, 15739, 16069, 18049, 18919, 19429, 21019, 22279, 25309, 31729, 34849, 43789, 51349, 55339, 62989, 67219, 69499, 72229, 77269, 79699, 81049, 82729, 88819, 97849, 99139, 101119, 109849, 116539, 119299, 122209, 135469, 144169, 157279, 165709, 166849, 171169, 187639, 194869, 195739, 201499, 201829, 217369, 225349, 240049, 243709, 247609, 247999, 257869, 260419, 266689, 268819, 276049, 284749, 285289, 294319, 295879, 299479, 300499, 301999, 326149, 334429, 340939, 346399, 347989, 354259, 358909, 361219, 375259, 388699, 389569, 392269, 394819, 397549, 397759, 402139, 402769, 412039, 419059, 420859, 427249, 442579, 444349, 452539, 463459, 465169, 467479, 470089, 477019, 490579, 495619, 500239, 510619, 518809, 536449, 536779, 539509, 549169, 559219, 563419, 570049, 572659, 585919, 594829, 597679, 607309, 622249, 626629, 632089, 632329, 633469, 633799, 654169, 657499, 661099, 663589, 664669, 666439, 680299, 681259, 691729, 705169, 715159, 734479, 736369, 739399, 768199, 773029, 795799, 803449, 814069, 822169, 823729, 829729, 833719, 837079, 845989, 854929, 855739, 857959, 875269, 876019, 881479, 889879, 907399, 930079, 938059, 946669, 954979, 958549, 959479, 976309, 978079, 983449, 1002349, 1003369, 1006309, 1006339, 1008859, 1015369, 1022389, 1022509, 1023949, 1027759, 1043599, 1063969, 1065019, 1068259, 1068709, 1091269, 1093069, 1093999, 1100839, 1117609, 1117819, 1118869, 1120549, 1121839, 1122139, 1126669, 1137889, 1146799, 1155619, 1156039, 1157839, 1163719, 1167709, 1168249, 1170139, 1172029, 1172539, 1173589, 1182289, 1210879, 1228399, 1230379, 1233439, 1246249, 1246369, 1257079, 1272289, 1285519, 1298119, 1322179, 1322599, 1324579, 1329709, 1337269, 1339909, 1340329, 1351249, 1352209, 1358809, 1360789, 1368469, 1381279, 1400809, 1402369, 1410979, 1440589, 1447009, 1451839, 1461409, 1468639, 1508629, 1514329, 1524079, 1525969, 1540969, 1571749, 1573549, 1573939, 1577299, 1584439, 1588759, 1592869, 1603339, 1615849, 1616809, 1621729, 1627609, 1631059, 1653109, 1659109, 1670569, 1678759, 1681879, 1685449, 1691869, 1711819, 1718869, 1727779, 1747729, 1748479, 1749499, 1755829, 1764229, 1780489, 1791739, 1797379, 1798639, 1802659, 1819849, 1830349, 1833529, 1834039, 1837399, 1857679, 1890529, 1902619, 1904479, 1910269, 1912069, 1912459, 1915939, 1917739, 1925389, 1943659, 1954159, 1954369, 1959319, 1979149, 1979899, 2002339, 2007619, 2007919, 2016409, 2020729, 2050339, 2062009, 2063779, 2065579, 2075839, 2079199, 2083519, 2084449, 2087389, 2107669, 2116579, 2136139, 2141809, 2143489, 2144509, 2157739, 2159239, 2168659, 2176639, 2177509, 2193889, 2202799, 2203969, 2223679, 2225059, 2246149, 2248249, 2256349, 2262979, 2266639, 2289649, 2290039, 2294059, 2303599, 2340259, 2342779, 2362279, 2373409, 2376169, 2381089, 2403889, 2413429, 2418679, 2423419, 2443789, 2458669, 2470339, 2478529, 2479669, 2499949, 2508049, 2535109, 2541949, 2546239, 2552119, 2552659, 2561269, 2564329, 2576599, 2594959, 2594989, 2596669, 2604739, 2614069, 2635489, 2668249, 2673529, 2674549, 2679499, 2683789, 2696929, 2704909, 2712379, 2715289, 2728549, 2731699, 2731909, 2759299, 2761729, 2764129, 2790259, 2805169, 2822719, 2839939, 2840269, 2846869, 2849689, 2875339, 2879299, 2893489, 2918569, 2927599, 2927809, 2952799, 2954689, 2989039, 2990839, 3047419, 3058879, 3062209, 3063499, 3066829, 3076399, 3089329, 3092569, 3101479, 3103279, 3129619, 3153589, 3157579, 3171739, 3187609, 3200209, 3207439, 3208819, 3215749, 3224869, 3243349, 3277699, 3295549, 3308959, 3326629, 3328909, 3340879, 3366829, 3371449, 3374479, 3378049, 3400219, 3416059, 3436249, 3437719, 3467539, 3479899, 3512059, 3512239, 3512989, 3513079, 3514549, 3518329, 3550699, 3584929, 3586909, 3593509, 3621469, 3652939, 3669769, 3690529, 3713449, 3727729, 3735169, 3741169, 3798079, 3817819, 3837139, 3837859, 3849829, 3854119, 3894049, 3919219, 3919

C++: #include<stdio.h>
#include<iostream>
#include<algorithm>
#include<deque>

using namespace std;

void MakePrimeArray(deque<bool>& A,int n){
	
	A[0] = A[1] = false;
	for(int i=2;i<n;i++){
		A[i] = true;
	}
	
	for(int	i=2;i*i<n;i++){
	if(A[i]){
			for(int j=i*i;j<n;j+=i){
				A[j] = false;
			}
		}
	}
	
}

void yotuko(deque<int>& A){
	deque<int>::iterator it=A.begin();
	for(int i=0;i<A.size()-3;i++){
		if((*(it+1)==((*it)+2)&&(*(it+2))==(*it+6))&&(*(it+3)==(*it+8)))
			A.erase(it);
		else
			it++;
	}
}


int main(){
	
	int n=10000001;

	deque<bool> primearray;
	
	primearray.resize(n);
	
	MakePrimeArray(primearray,n);
	/*
	deque<int> prime;
	
	for(int i=13;i<n;i++){
		if(primearray[i]){
			prime.push_back(i);
		}
	}
	
	yotuko(prime);
*/
	while(true){
		int innum;
		cin >> innum;
		//scanf("%d",&innum);
		
		if(innum==0) break;
		
		int answer=0;
		answer=innum;
		while(true){
			if(primearray[answer]&&primearray[answer-2]&&primearray[answer-6]&&primearray[answer-8]){
				break;	
			}
			answer--;
		}
		cout << answer << endl;
	}
	
	return 0;
}

C++: #include<iostream>
#include<vector>

using namespace std;

int main()
{
	int n;
	int i;
	vector<char> prime;
	
	for(i=0;i<10000000;i++)
	{
		prime.push_back('1');
	}
	
	prime[0]=prime[1]='0';
	
	for(i=0;i<10000000;i++)
	{
		if(prime[i]=='1')
		{
			for(int j=2;j*i<10000000;j++)
			{
				prime[j*i]='0';
			}
		}
	}
	for(i=0;i<10000000;i++)
	{
		if(i+8<10000000)
		{
			if((prime[i]=='1' || prime[i]=='2') && (prime[i+2]=='1' || prime[i+2]=='2') && (prime[i+6]=='1' || prime[i+6]=='2') && (prime[i+8]=='1' || prime[i+8]=='2'))
			{
				prime[i+8]='2';
			}
		}
	}
	
	for(;;)
	{
		cin >> n ;
		if(n==0)
			break;
		
		for(;prime[n]!='2';--n)
		{
		}
		cout << n << endl;
	}
}

C++: #include <iostream>
using namespace std;

void prime(bool is_prime[]){
	is_prime[0]=is_prime[1]=false;
	for(int i=2; i<1000000; i++){
		is_prime[i]=true;
	}

	for(int i=2; i*i<1000000; i++){
		if(is_prime[i]){
			for(int j=i*i; j<1000000; j+=i){
				is_prime[j]=false;
			}
		}
	}
};

int main(){
	bool is_prime[1000000];

	prime(is_prime);

	}
	while(true){
		int a;
		cin>>a;
		if(a==0)
			break;

		int ans=0;
		for(int i=a; i>=13; i--){
			if(is_prime[i]){
				if(is_prime[i-2]){
					if(is_prime[i-6]){
						if(is_prime[i-8]){
							ans=i;
							break;
						}
					}
				}
			}
		}
		cout<<ans<<endl;
	}
	return 0;
}

C++: #include<iostream>
#include<string>
#include<algorithm>
#include<map>
#include<set>
#include<utility>
#include<vector>
#include<cmath>
#include<cstdio>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mp make_pair
#define it ::iterator
#define all(in) in.begin(),in.end()
const double PI=acos(-1);
const double ESP=1e-10;
using namespace std;
#define MAX 10000010
bool num[MAX]={1,1,0};
int main(){
  for(int i=3;i<MAX;i+=2){
    if(num[i]==1)
      continue;
    for(int j=3*i;j<MAX;j+=i*2)
      num[j]=1;
  }
  for(int i=4;i<MAX;i+=2)num[i]=1;

  vector<long long int>ans;
  loop(i,13,MAX){
    if(!(num[i]||num[i-2]||num[i-6]||num[i-8]))ans.pb(i);
  }
  ans.pb(100000000);
  sort(all(ans));
  int in;
  while(cin>>in,in){
    int k;
    rep(i,ans.size())if(ans[i]>in){k=i-1;break;}
    cout<<ans[k]<<endl;
  }
}

C++: using namespace std;
#include <iostream>
#include <string>
#include <set>
#include <functional>
#include <vector>
#include <algorithm>
#include <stdio.h>
#include <math.h>
bool is_pr[10000001];
bool ans[10000001]={};
int mans[10000001]={};
int d[]={0,-2,-6,-8};
int main()
{
	fill(is_pr,is_pr+10000001,true);
	for(int i=2;i<=4000;i++){
		if(is_pr[i])for(int j=2;j*i<=10000000;j++)is_pr[i*j]=false;
	}
	for(int i=13;i<=10000000;i++){
		bool tmp=true;
		for(int j=0;j<4;j++)tmp&=is_pr[i+d[j]];
		ans[i]=tmp;
	}
	for(int i=13;i<=10000000;i++){
		if(ans[i])mans[i]=i;
		else mans[i]=mans[i-1];
	}
	int num;
	while(cin>>num&&num){
		cout<<mans[num]<<endl;
	}
    return 0;
}