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  1. #include <iostream>
  2. #include <vector>
  3. using namespace std;
  4.  
  5. int main() 
  6. {
  7. 	const int N = 2e7;
  8.  
  9. 	vector <long long> is_prime(N, true);
  10. 	is_prime[0] = is_prime[1] = false;
  11.  
  12. 	vector <long long> primes;
  13.  
  14. 	for(long long i = 2; i < N; i++)
  15. 	{
  16. 	      if(is_prime[i]) primes.push_back(i);
  17.  
  18. 	      for(int j = 0; j < primes.size() && i*primes[j] < N; j++)
  19. 	      {
  20. 	               is_prime[i*primes[j]] = false;
  21.  
  22. 	               if(i%primes[j] == 0) break;
  23. 	      }
  24. 	}
  25.  
  26. 	cout << primes.size();
  27.  
  28. 	return 0;
  29. }
Success #stdin #stdout 0.26s 15232KB
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https://ideone.com/53UlQ6
language:
C++ (gcc 8.3)
created:
5 years ago
visibility:
secret

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