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>
#include <cstring>
#include <algorithm>
using namespace std;

int main()
{
  const int MAX_PRIME = 10000000+1;

  static bool p[MAX_PRIME];
  memset(p, true, sizeof(p));
  p[0] = p[1] = false;
  for (int i = 2; i*i <= MAX_PRIME; ++i) {
    if (p[i]) {
      for (int j = i+i; j < MAX_PRIME; j += i)
	p[j] = false;
    }
  }

  vector<int> prime;
  for (int i = 0; i < MAX_PRIME; ++i) {
    if (p[i])
      prime.push_back(i);
  }

  vector<int> ans;
  for (unsigned int i = 3; i < prime.size(); ++i) {
    if (prime[i-3]+8 == prime[i] &&
	prime[i-2]+6 == prime[i] &&
	prime[i-1]+2 == prime[i])
      ans.push_back(prime[i]);
  }

  int n;
  while (cin >> n) {
    if (n == 0)
      break;
    cout << *(upper_bound(ans.begin(), ans.end(), n)-1) << endl;
  }
  return 0;
}

C++: #include<bits/stdc++.h>

using namespace std;

bool PrimeNumber[10000001];
int Ans[10000001];


void solve() {
	memset(PrimeNumber, true, sizeof(PrimeNumber));
	PrimeNumber[0] = PrimeNumber[1] = false;

	for (int i = 2; i*i < 10000001; ++i) {
		if (!PrimeNumber[i]) {
			continue;
		}
		for (int j = i*i; j < 10000001; j+=i) {
			PrimeNumber[j] = false;
		}
	}

	Ans[13] = 13;
	for (int i = 14; i < 10000001; ++i) {
		Ans[i] = Ans[i - 1];
		if (PrimeNumber[i] && PrimeNumber[i - 2] && PrimeNumber[i - 6] && PrimeNumber[i - 8]) {
			Ans[i] = i;
		}
	}
}

int main() {
	int n;

	solve();
	while (cin >> n, n) {
		cout << Ans[n] << endl;
	}

	return 0;
}

C++: #include<iostream>
using namespace std;
#define N 10000000
bool P[N + 1];
void eratos(){
for ( int i = 0; i <= N; i++ ) P[i] = true;
P[0] = P[1] = false;
for ( int i = 2; i*i <= N; i++ )
if ( P[i] )
for ( int j = 2; i*j <= N; j++ ) P[i*j] = false;
}
int getQuads(int n){
for ( int i = n; i >= 13; i--)
if ( P[i] && P[i-2] && P[i-6] && P[i-8] ) return i;
}
int main(){
eratos();
int n;
while( cin >> n && n ) cout << getQuads(n) << endl;
return 0;
}

C++: #include<iostream>
#include<math.h>
#define MN 10000001
using namespace std;

bool prime[MN];

int main()
{
  prime[0] = prime[1] = true;
  for(int i = 2; i < sqrt(MN) + 1; i++)
  {
    if(prime[i])
      continue;
    for(int j = i + i; j < MN; j += i)
      prime[j] = true;
  }
loop:
  int N;
  cin >> N;
  if(!N)
    return 0;
  for(int i = N; i >= 0; i--)
  {
    if(!(prime[i - 8] || prime[i - 6] || prime[i - 2] || prime[i]))
    {
      cout << i << endl;
      break;
    }
  }
  goto loop;
}

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

int prime[1000000];
int prime4[1000000];
int GetPrime( int n );
int GetPrime4( int pcnt );

int main(){
	int i,n;
	int pcnt,p4cnt;
	pcnt = GetPrime( 7000000 );
	//cout << pcnt << endl;
	p4cnt = GetPrime4( pcnt );

	while( cin >> n ){
		if( n == 0 )
			break;
		//2分探索
		int start = 0,last = p4cnt-1,medi;
		while( start <= last )
		{
			medi = (start+last) >> 1;
			if( prime4[medi] == n ){
				break;
			}
			if( prime4[medi] > n )
			{
				last = medi-1;
			}
			if( prime4[medi] < n )
			{
				if( prime4[medi+1] > n )break;
				if( prime4[medi+1] == n ){
					medi++;
					break;
				}
				start = medi+1;
			}
		}
		cout << prime4[medi] << endl;
	}
	return 0;
}

int GetPrime(int n){
	int i,j;

	int cnt = 0;
	for( i = 2;i <= n;i++ ){
		for( j = 0;j < cnt;j++ ){
			if( i%prime[j] == 0 )
				break;
			if( prime[j] * prime[j] > i ){
				j = cnt;
				break;
			}
		}
		if( j == cnt ){
			prime[cnt] = i;
			cnt++;
		}
	}
	return cnt;
}

int GetPrime4( int pcnt ){
	int i;
	int cnt = 0;
	for( i = 0;i < pcnt-3;i++ ){
		if( prime[i+1] - prime[i] == 2 && prime[i+2] - prime[i+1] == 4 && prime[i+3] - prime[i+2] == 2 ){
			prime4[cnt] = prime[i+3];
			cnt++;
			i++;
		}
	}
	return cnt;
}