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>

// Begin {{{
using namespace std;

#define all(x) x.begin(), x.end()
#define rep(i, n) for (i64 i = 0; i < (n); ++i)
#define reps(i, s, n) for (i64 i = (s); i <= (n); ++i)
#define VAR(Type, ...) Type __VA_ARGS__; IN(__VA_ARGS__)
#define Float(x) OUTN(fixed, setprecision(x));

using i64 = int_fast64_t;
using pii = pair<i64, i64>;

template <class A, class B>
inline bool chmax(A &a, const B &b) { return b > a && (a = b, true); }

template <class A, class B>
inline bool chmin(A &a, const B &b) { return b < a && (a = b, true); }

constexpr int INF = 0x3f3f3f3f;
constexpr i64 LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr int MOD = int(1e9) + 7;

// IN
void IN() {}
template <class Head, class... Tail>
void IN(Head&& head, Tail&&... tail) {
  cin >> head;
  IN(forward<Tail>(tail)...);
}

// OUTS
void OUTS() {}
template <class Head, class... Tail>
void OUTS(Head&& head, Tail&&... tail) {
  cout << head << " \n"[sizeof...(tail)==0];
  OUTS(forward<Tail>(tail)...);
}

template <class T>
void OUTS(vector<T> &vec) { for (auto &e : vec) cout << e << " \n"[&e==&vec.back()]; }

template <class T>
void OUTS(vector<vector<T>> &df) { for (auto &vec : df) OUTS(vec); }

// OUTL
void OUTL() {}
template <class Head, class... Tail>
void OUTL(Head&& head, Tail&&... tail) {
  cout << head << "\n";
  OUTL(forward<Tail>(tail)...);
}

template <class T>
void OUTL(vector<T> &vec) { for (auto &e : vec) cout << e << "\n"; }

// OUTN
void OUTN() {}
template <class Head, class... Tail>
void OUTN(Head&& head, Tail&&... tail) {
  cout << head;
  OUTN(forward<Tail>(tail)...);
}

template <class T>
void OUTN(vector<T> &vec) { for (auto &e : vec) cout << e; }
// }}} End

vector<bool> isPrime;

void sieve(int MAX) {
  if (MAX + 1 > isPrime.size()) isPrime.resize(MAX + 1, true);
  isPrime[0] = false;
  isPrime[1] = false;
  for (int i = 2; i * i <= MAX; ++i) {
    if (isPrime[i]) {
      for (int j = 2; i * j <= MAX; ++j) isPrime[i*j] = false;
    }
  }
}

signed main()
{
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  sieve(10000010);

  int n;
  while (IN(n), n) {
    for (int i = n; i >= 13; --i) {
      if (isPrime[i] && isPrime[i-2] && isPrime[i-6] && isPrime[i-8]) {
        OUTL(i);
        break;
      }
    }
  }

  return 0;
}

C++: // 2010/07/20 Tazoe

#include <iostream>
using namespace std;

void eratos(bool prm[], int n)
{
	if(n>=1)
		prm[0] = false;
	if(n>=2)
		prm[1] = false;

	for(int i=2; i<n; i++)
		prm[i] = true;

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

int main()
{
	bool prm[10000001];
	eratos(prm, 10000001);

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

		for(int i=n; i>=13; i--)
			if(prm[i]&&prm[i-2]&&prm[i-6]&&prm[i-8]){
				cout << i << endl;
				break;
			}
	}

	return 0;
}

C++: #include <iostream>
#define rep2(x,from,to) for(int x=(from);(x)<(to);(x)++)
#define rep(x,to) rep2(x,0,to)
using namespace std;

int main(){
	bool p[1000001] = {};
	p[0] = p[1] = 1;
	rep2(i,2,1001) {
		if(!p[i]) {
			for(int j = 2*i; j<=1000000; j+=i) {
				p[j] = 1;
			}
		}
	}
	int n;
	while(cin >> n, n) {
		for(int i = n; i >= 13; i--) {
			if(!p[i] && !p[i-2] && !p[i-6] && !p[i-8]) {
				cout << i << endl;
				break;
			}
		}
	}
}

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

int prime(int a) {
	if (a % 2 == 0)return false;
	if (a % 3 == 0)return false;
	for (int b = 5; b < a; b+=2) {
		if (a % b == 0)return false;
		if ((b + 1)*(b + 1) > a)return true;
	}
}
int main() {
	while (1) {
		int a;
		cin >>a;
		if (a == 0)break;
		for (int b = a - (a % 6) + 1;; b -= 6) {
			if (prime(b) && prime(b - 2) && prime(b - 6) && prime(b - 8)) { cout << b << endl; break; }
		}
	}
}