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  1. #include <iostream>
  2. #include <vector>
  3.  
  4. using namespace std;
  5.  
  6. const int M = 1000067;
  7. bool pie[M];
  8.  
  9. void sito() {
  10.     for (int i = 2; i < M-1; i++) {
  11.         pie[i] = true;
  12.     }
  13.     pie[0] = pie[1] = false;
  14.     for (int p = 2; p * p < M; p++) {
  15.         if (pie[p]!=0) {
  16.             for (int i = p * p; i < M; i += p) {
  17.                 pie[i] = false;
  18.             }
  19.         }
  20.     }
  21. }
  22.  
  23. int main() {
  24.     ios_base::sync_with_stdio(0);
  25.     cin.tie(0);
  26.  
  27.     sito();
  28.  
  29.     long int n;
  30.     cin>>n;
  31.  
  32.     long long l2 = 0;
  33.     long long war = 0;
  34.  
  35.     for (int i = 0; i < n; i++) {
  36.         int a;
  37.         cin >> a;
  38.         if (a == 2) 
  39.             l2++;
  40.          else if (pie[a + 2]==1) 
  41.             war++;
  42.  
  43.     }
  44.  
  45.     cout << l2 * war << "\n";
  46.  
  47.     return 0;
  48. }
Success #stdin #stdout 0.01s 5304KB
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https://ideone.com/BiRuPV
language:
C++14 (gcc 8.3)
created:
1 hour ago
visibility:
public

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