The prime number in nod 1181 prime (prime number Sieve method)

1181 prime number in prime number (prime number Sieve) topic Source: Sgu Base time limit: 1 second space limit: 131072 KB score: 0 Difficulty: Basic collection concern If a prime number is a primes, the numbers in the list are also prime numbers, so it is called prime numbers in prime numbers. For example: 3 5 are prime numbers for the 2nd and 3rd respectively, so they are prime numbers in prime numbers. Now give a number n, and find out how many prime numbers are in the smallest prime numbers of >=n (which can be considered by the prime sieve method). Input

Enter a number n (n <= 10^6)

Output

The output >=n the prime number in the smallest prime number.

Input example

20

Output example

31

#include <bits/stdc++.h>
const int maxn=1e6+200;
using namespace std;
BOOL A[maxn]={false};
int main ()
{
    long long n,i,j;
	Long long ans=0;
	cin>>n;
	A[1]=true;
	for (i=2; i<maxn; i++)
	{
		if (!a[i])
		{
			ans++;
			if (!a[ans]&&i>=n)
			{
				cout<<i<<endl;
				break;
			}
			for (j=i*i; j<maxn; j+=i)
			a[j]=true;
		}
	}
	return 0;
}