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<iostream>
#include<vector>

int main(){
	const int MAX_N = 10000000;
	int *is_prime = new int[MAX_N+1];
	std::vector<int> quad;

	for(int i=0;i<=MAX_N;i++){
		is_prime[i] = 1;
	}

	is_prime[1] = 0;

	for(int i=2;i<=10000000;i++){
		if(is_prime[i]){
			if(i-8 >= 2 && is_prime[i-8] &&
				 is_prime[i-6] && is_prime[i-2]){//4つ子素数か
				quad.push_back(i);
			}

			for(int j=i*2;j<=MAX_N;j+=i){
				is_prime[j] = 0;
			}
		}
	}

	int n;
	while(std::cin >> n, n){
		for(int i=quad.size()-1;i>=0;i--){
			if(quad[i] <= n){
				std::cout << quad[i] << std::endl;
				break;
			}
		}
	}
}

C++: #include<stdio.h>
int n;
int a[10000001];
int i,j;

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

  for(i=10000000;i>=13;i--){
    if(a[i]==1&&a[i-2]==1&&a[i-6]==1&&a[i-8]){
      a[i]=i;
    }else{
      a[i]=0;
    }
  }

  for(i=14;i<=10000000;i++){
    if(a[i]==0)a[i]=a[i-1];
  }

  while(1){
    scanf("%d",&n);
    if(n==0)break;
    printf("%d\n",a[n]);
  }
  
  return 0;
}

C++: #include<stdio.h>
#include<math.h>
#include<iostream>
using namespace std;

int main(){
	int *p,n,i,j,k,a,c=0,t=1,y;
	scanf("%d", &n);
	while (n>0){
	p = new int[n];
	
		for (i = n; i > 1; i--){
			for (j = 3; j < sqrt(i); j+=2){
				if (i%j == 0){
					t = 0;
				}
			}
				if (t==1){
					p[c] = i;
					c++;
				}
				t = 1;
		}
		for (i = 0; i < c-3;i++){
			if (p[i] - 2 == p[i + 1] && p[i] - 6 == p[i + 2]&&p[i]-8&&p[i+3]){
				printf("%d\n",p[i]);
				break;
			}
		
		}
		scanf("%d",&n);
	}
}

C++: #include <bits/stdc++.h>
using namespace std;
#define FOR(i, s, n) for(int i = s; i < (int)n; i++)
#define per(i, n) for(int i = n; i >= 0; i--)
#define ROF(i, s, n) for(int i = s; i >= (int)n; i--)
#define FORIT(i, A) for (auto i : A)
#define PRINT(x) cout << (x) << "\n"
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define MP make_pair
#define EACH(i, n) for (__typeof((n).begin()) i = (n).begin(); i != (n).end(); ++i)
#define SZ(a) int((a).size())
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define CLR(a) memset((a), 0 ,sizeof(a))
#define dump(x) cout << #x << " = " << (x) << "\n";
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << "\n";
#define sq(n) (n) * (n)
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef priority_queue<int> maxpq;
typedef priority_queue< int, vector<int>, greater<int> > minpq;
static const double EPS = 1e-10;
static const double PI = acos( -1.0 );
static const int mod = 10007;
static const int INF = 1 << 25;
static const LL LL_INF = 1152921504606846976;
static const int dx[] = { -1, 0, 1, 0,  1, -1,  1, -1 };
static const int dy[] = { 0, -1, 0, 1 , 1,  1, -1, -1 };

VI pm;
int n;

int main() {
	vector<bool> is_pm( 10000000, true );
	for ( int i = 3; i * i <= 10000000; i += 2 ) {
		if ( is_pm[ i ] ) {
			for ( int j = i * i; j < 10000000; j += i ) {
				is_pm[ j ] = false;
			}
		}
	}
	while ( ~scanf("%d", &n) && n ) {
		if ( n % 2 == 0 ) {
			n--;
		}
		for ( int i = n; i >= 13; i -= 2 ) {
			if ( is_pm[ i ] && is_pm[ i - 2 ] && is_pm[ i - 6 ] && is_pm[ i - 8 ] ) {
				printf( "%d\n", i );
				break;
			}
		}
	}
	return 0;
}