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#include<iostream>
#include<cmath>
using namespace std;
int main()
{
    int l=1,u=20000000,d,j;
    
    
    d=u-l+1;
    bool *flag=new bool[d];
    for (int i=0;i<d;i++)
    flag[i]=true;
    for (int i=(l%2!=0);i<d;i+=2)
    flag[i]=false;
    for (int i=3;i<=sqrt(u);i+=2)
    {
        j=l;
        while (j%i!=0)
        j++;
        for (j=j+i;j<u;j+=i)
        flag[j-l]=false;
        }
               
  if (l<=1) flag[1-l]=false;
  if (l<=2) flag[2-l]=true;

  
  int c=1;
  int b[110002];
  for (int i=0;i<d;i++) if (flag[i] && flag[i+2]) 
  {
    
       b[c-1]=i+l;
      
      
      c++; 
     
  }
  
 int n;               
 while (cin>>n)
 {
     
            int t=b[n-1];
            cout<<"("<<t<<", "<<t+2<<")"<<endl;
 }
return 0;
}

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#include <stdio.h> 
#include<math.h>



long int ar[100005],t,t1 ;
char   arr[200000005];

void get_prime(long int n)

{

	long int x ;
	//char   arr[20000005];
	long int k=1,l;

	for (x =1 ; x <= n ; x++)
	{
		arr[x]='0';
	}

	while( k <= sqrt(n))
	{
		if(arr[k] == '1' ||k==1)
		k++;

		else 
		{
			for(int i=2 ; l<=n ;i++ )
			{
				l=i*k;
				arr[l] = '1';

			}
			l =0;
			k++;
		}
	}
	
	t=0;
	t1=0;
	for(k=3 ;k <=n; k++)
	{
	   if(arr[k]!='1' &&((arr[k+2] != '1') || (arr[k-2] != '1')))
	   {
			  ar[t1] = k;
			  t1++;
	   }
	}

}



int main()
{ 
	get_prime(20000000);

	long int n;
	while(scanf("%ld",&n)==1)
	{
		printf("(%ld, %ld)\n",ar[n-1],ar[n]);
	}
	return 0;
}

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gprime[j] = 1; // for(j = i * i; j <= 20000000;j+=i) so j can be 20000000, but you declared gprime[1000000]

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#include<iostream>
#include<cmath>
using namespace std;
bool prime[18409202];
void seive()
{
     int m=4290;
     memset(prime,true,sizeof(prime));
     prime[0]=false;
     prime[1]=false;
     for(int i=2;i<=m;i++)
     if(prime[i]) for(int k=i*i;k<=18409202;k+=i)
                  prime[k]=false;
}
int main()
{
    
    seive();
    long i,count,s;
    while(cin>>s) 
    {
                 if(s==1)
                 cout<<"(3, 5)"<<endl;
                 else if(s>1)
                 {
                         count=1;i=5;
                         while(count!=s)
                         {
                                        if(prime[i] && prime[i+2])
                                        count++;
                                        i=i+6;
                         }
                        cout<<"("<<i-6<<", "<<i-4<<")"<<endl;
                 }
    }
    system("pause");
    } 

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At Last AC in 1.4 sec

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#include<stdio.h>
#include<math.h>

long long a[100000],c,flag[1000000],b[10000][100];

void seive(long long n)
{
	long long k,i,j,r;
	k=sqrt(n);
	for(i=1;i<=n;i++)
		flag[i]=0;
	flag[1]=1;
	a[0]=2;
	c=1;
	for(i=4;i<=n;i+=2)
		flag[i]=1;
	for(i=3;i<=n;i+=2)
	{
		if(flag[i]==0)
		{
			a[c++]=i;
			if(k>=i)
			{
				r=i+i;
				for(j=i*i;j<=n;j+=r)
					flag[j]=1;
			}
		}
	}
	a[c]=0;
}

int main()
{ 
	long long n,f,i,p,j;
	seive(2000000);
	while(scanf("%lld",&n)==1&&n>0)
	{
		f=0;
		j=0;
		for(i=1;i<c;i++)
		{
			if(a[i]-2==a[i-1])
			{
				b[j][0]=a[i-1];
				b[j][1]=a[i];
				j++;
			}
			if(j==n)
				break;
		}
		printf("(%lld, %lld)\n",b[j-1][0],b[j-1][1]);
	}
	return 0;
}