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<bits/stdc++.h>
using namespace std;
int F[11451419];
#define EPS 1e-14
bool prime(int p){
    if(F[p]==0)return false;
    if(F[p]==1)return true;
     
    for(int i=2;i*i<=p;i++){
    	if(F[i]==0)continue;
        if(p%i==0){
	        F[p]=0;
	        return false;
        }
    }
    F[p]=1;
    return true;
}
int main()
{
for(int i=1;i<=10000000;i++)F[i]=-1;
    while(true){
        int N;
        scanf("%d",&N);
        if(N==0)break;
        if(N>=13&&N<=18){
            printf("13\n");
            continue;
        }
        while(true){
            if(N%10!=9){
                N--;
                continue;
            }
            if(N%3!=1){
            	N--;
            	continue;
            }
            if(prime(N)&&prime(N-2)&&prime(N-6)&&prime(N-8)){
                printf("%d\n",N);
                break;
            }
            else N-=10;
        }
    }
    return 0;
}

C++: #include "bits/stdc++.h"
#include<unordered_map>
#include<unordered_set>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
template<class T>
using Table = vector<vector<T>>;
const ld eps=1e-9;

//// < "D:\D_Download\Visual Studio 2015\Projects\programing_contest_c++\Debug\a.txt"

long long int powmod(long long int a, long long int b, const int mod) {
	assert(b >= 0);
	if (b == 0)return 1;
	if (b == 1)return a;
	long long int ans = 1;
	long long int aa = powmod(a, b / 2, mod);
	ans *= aa*aa;
	ans %= mod;
	if (b % 2)ans *= a;
	ans %= mod;
	return ans;
}

const int k = 20;
//?´???°??????
bool mirror_rabin(const long long int n) {
	if (n == 2)return true;
	if (n == 1 || (n & 1) == 0)return true;
	int s = 0;
	int d = n - 1;
	while (!(d % 2)) {
		s++;
		d /= 2;
	}
	for (int i = 0; i < k; ++i) {
		const long long int a = rand() % (n - 1) + 1;
		long long int t = d;
		long long int y = powmod(a, t, n);
		while (t != n - 1 && y != 1 && y != n - 1) {
			y = (y*y) % n;
			t <<= 1;
		}
		if (y != n - 1 && (t & 1) == 0)return false;
	}
	return true;
}
bool isso(long long int a) {
	return mirror_rabin(a);
	if (a == 1 || a == 0)return false;
	for (long long int i = 2; i*i <= a; ++i) {
		if ((a%i)) {
		}
		else {
			return false;
		}
	}
	return true;
}


int main() {
	while (1) {
		int N; cin >> N;
		if (!N)break;
		int num = N;
		while (num % 6 != 1)num--;
		while (1) {
			if (isso(num) && isso(num - 2) && isso(num - 6) && isso(num - 8)) {
				cout << num << endl;
				break;
			}
			num-=6;
		}

	}
	return 0;
}

C++: #define MAX 10000000
int  p[MAX];
int  four[1000];
int main(void)
{
  int i,j,f=0;
  //ツ倍ツ青板づーツ渉慊外
  for(i=2 ; i<=MAX/2 ; i++){
      for(j=2 ; i*j<=MAX ; j++){
	if(p[i*j] == 0)
	  p[i*j] = 1;
      }
  }

  for(i=3 ; i < MAX-7 ; i+=2){
    if(p[i] == 0 && p[i+2]==0 && p[i+6]==0 && p[i+8]==0)
      {
	four[f++]=i+8;
	//	printf("%d\n",i+8);
      }
  }
  
  for(;scanf("%d",&j),j;)
    {
      for(i=0 ;four[i]<=j; i++);
      printf("%d\n",four[i-1]);
    }
  
  return 0;
}

C++: //エラトステネスの篩

#include<iostream>
using namespace std;

int prime[10000000];

int main()
{

    for(int i=0; i<10000000; i++){
      prime[i] = i+1;
      if(i==0)
        prime[0] = 0;
    }
    
    for(int i=1; i<10000000; i++){     
      if(prime[i]!=0){
         i++;
        for(int j=2; i*j<10000000; j++){
          prime[i*j-1] = 0;
         }
         i--;  
       } 
     }




  while(1){
  
    int n;
    
    cin >> n;
    
    if(n==0)
      return 0;
       
     while(n>=13){
       if(prime[n-1]!=0 && prime[n-3]!=0 && prime[n-7]!=0 && prime[n-9]!=0){
         cout  << prime[n-1] << endl;
         break;
       }
       n--;
     }
     
  } 
    
    
    


}