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>
using namespace std;
const int SIZE = 10000000;
bool isprime[SIZE + 1];
vector<int> prime;
void make_prime(){
    for(int i = 2; i <= SIZE; i++){
        isprime[i] = true;
    }
    isprime[0] = false;
    isprime[1] = false;
    for(int i = 2; i <= SIZE; i++){
        if(isprime[i] == false) continue;
        for(int j = i * 2; j <= SIZE; j += i){
            isprime[j] = false;
        }
        prime.push_back(i);
    }
}

vector<int> yotugo;
void make_list(){
    for(int i = 0; i <= (prime.size() - 4); i++){
        if(prime[i + 1] == (prime[i] + 2) && prime[i + 2] == (prime[i] + 6) && prime[i + 3] == (prime[i] + 8)){
            yotugo.push_back(prime[i + 3]);
        }
    }
}

int check(int n){
    int i;
    for(i = 0; yotugo[i] <= n && i < yotugo.size(); i++) ;
    return yotugo[i - 1];
}

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

C++: #include<bits/stdc++.h>
using namespace std;

vector<int>pr;
vector<int>Qpr;
bool isp[11451419];

void eratos(int mx){
	for(int i=0;i<=mx;i++)isp[i]=true;
	
	isp[0]=false;
	isp[1]=false;
	
	for(int i=2;i<=mx;i++){
		if(isp[i]){
			pr.push_back(i);
			for(int j=2*i;j<=mx;j+=i)isp[j]=false;
			}
		}
		return ;
	}

int main(){
	eratos(11451400);
	for(int i=3;i<pr.size();i++){
			int a=pr[i-3];
			int b=pr[i-2];
			int c=pr[i-1];
			int d=pr[i];
			
			if(b-a==2&&c-b==4&&d-c==2)Qpr.push_back(d);
			}
	int n;
	while(cin>>n,n){
		int ans=0;
		
		for(int i=0;i<Qpr.size();i++){
			if(Qpr[i]>n)break;
			ans=Qpr[i];
			}
			cout<<ans<<endl;
		}
		return 0;
	}

C++: #include<iostream>
#include<string>
#include<math.h>
using namespace std;
bool isprime(int);
int main() {
	int n;
	while(1){
		cin>>n;
		if(n==0)break;
		for(int i=n;i>=13;--i){
			if(isprime(i)&&isprime(i-2)&&isprime(i-6)&&isprime(i-8)){
				cout<<i<<endl;
				break;
			}
		}

	}
    return 0;
}
bool isprime(int a){
	if(a%2==0)return false;
	for(int i=3;i<=sqrt((float)a);++i){
		if(a%i==0)return false;
	}
	return true;
}

C++: #include <bits/stdc++.h>
using namespace std;
bool prime[10000001];
int main() {
    for(long long int i=2;i<3162;i++)if(!prime[i])for(long long int j=i*2;j<10000001;j+=i)prime[j]=1;
    int n;
    while(cin>>n,n){
        for(;;n--){
            if(!prime[n]&&!prime[n-2]&&!prime[n-6]&&!prime[n-8]){
                cout<<n<<endl;
                break;
            }
        }
    }
}

C++: #include<iostream>
#include <algorithm>
using namespace std;
#define MAX_LIST 5000000



int main(){
	bool *prime=(bool *)malloc(sizeof(bool)*MAX_LIST);
	for(int i=0;i<MAX_LIST;i++){
		prime[i]=1;
	}
	prime[0]=prime[1]=0;
	for(int i=0;i*i<MAX_LIST;i++){
		if(prime[i]==1){ 
			for(int j=i*2;j<MAX_LIST;j=j+i){
				prime[j]=0;
			}
		}
	}
	int *primelist=(int *)malloc(sizeof(int)*MAX_LIST);
	int j=0;
	for(int i=0;i<MAX_LIST;i++){
		if(prime[i]==1){
			primelist[j]=i;
			j++;
			if(j>MAX_LIST-1){
				break;
			}
		}
	}
	int *prime_num=(int*)malloc(sizeof(int)*MAX_LIST);
	prime_num[0]=1;
	for(int i=1;i<MAX_LIST;i++){
		prime_num[i]=prime_num[i-1]+prime[i];
	}
	
	
	int n;
	while(cin>>n,n){
		int ans=0;
		int s;
		int num=prime_num[n];
		for(int i=num;i>0;i--){
			if(primelist[i]>n){
			}else{
				if((primelist[i]-primelist[i-1]==2)
					&&(primelist[i-2]-primelist[i-3]==2)
					&&(primelist[i-1]-primelist[i-2]==4)){
						ans=primelist[i];
						break;
				}
			}
		}
		
		cout<<ans<<endl;
	}
	return 0;
}