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 <algorithm>
#include <iomanip>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max()/32*15+208;

struct Prime { // Wheel factorization
    static constexpr int wheel[] = {4, 2, 4, 2, 4, 6, 2, 6},
            wheel2[] = {7, 11, 13, 17, 19, 23, 29, 31},
            wheel_sum[] = {0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3, 3, 3, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 7, 7};
    static inline int f(int n){ return (n-1)/30*8 + wheel_sum[(n-1)%30]; }
    static inline int g(int n){ return ((n-1) >> 3)*30 + wheel2[(n-1)&7]; }
    vector<int> primes;

    Prime(int M) {
        primes = {2, 3, 5};
        if(M < 7){
            while(!primes.empty() && M < primes.back()) primes.pop_back();
            return;
        }
        int n = f(M), m = g(n), k = f(int(floor(sqrt(M))));
        primes.reserve(3+max(0, (int)(n/(log(n)-1.12))));
        vector<bool> sieve(n+1, true);
        for (int i = 1; i <= k; ++i) {
            if(sieve[i]){
                ll p = g(i), q = p*p;
                int j = (i-1)&7;
                while(q <= m){
                    sieve[f(q)] = false;
                    q += wheel[j] * p;
                    j = (j+1)&7;
                }
            }
        }
        for (int i = 1; i <= n; ++i) {
            if(sieve[i]) primes.emplace_back(g(i));
        }
    }
};
constexpr int Prime::wheel[], Prime::wheel2[], Prime::wheel_sum[];


int main() {
    Prime x(10000001);
    vector<int> val;
    for (int i = 0; i+3 < x.primes.size(); ++i) {
        if(x.primes[i]+2 == x.primes[i+1]
        && x.primes[i+1]+4 == x.primes[i+2]
        && x.primes[i+2]+2 == x.primes[i+3]){
            val.emplace_back(x.primes[i+3]);
        }
    }
    int n;
    while(cin >> n, n){
        printf("%d\n", *--upper_bound(val.begin(),val.end(), n));
    }
    return 0;
}

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

bool is_prime(int n)
{
	for(int i=2;i*i<=n;i++)
		if(n%i==0)return false;
	return n != 1;
}

int solve(int n)
{
	for(int i=n;i>=0;i--){
		if(is_prime(i)){
			if(is_prime(i-2)){
				if(is_prime(i-6)){
					if(is_prime(i-8)){
							return i;
					}
				}
			}
			i--;
		}
	}
	return 0;
}

int main()
{
	int n;
	while(cin >> n){
		if(n == 0)
			break;
			cout << solve(n) <<endl;
	}
	return 0;
}

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

int main(){
   bool is_prime[1000000];
   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;
         }
      }
   }
   while(true){
      int n;
      cin >> n;
      if(n==0)
         break;
      for(int i=n;i!=0;i--){
         if(is_prime[i-8]&&is_prime[i-6]&&is_prime[i-2]&&is_prime[i]){
            cout << i << endl;
            break;
         }
      }
   }
   return 0;
}