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  1. #include <iostream>
  2. #include <bits/stdc++.h>
  3. #define Kirlos ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
  4. #define ll long long
  5. #define pb(k) push_back(k)
  6. #define fi first
  7. #define se second
  8. #define endl '\n'
  9. #define mp(x,y) make_pair(x,y)
  10. #define MOD 1000000007
  11. #define all(x) x.begin(), x.end()
  12. #define PI acos(-1)
  13. #define sin(x) sin((x)*PI/180)
  14. #define cos(x) cos((x)*PI/180)
  15. #define tan(x) tan((x)*PI/180)
  16. #define Ones(x) __builtin_popcountll(x)
  17.  
  18. using namespace std;
  19.  
  20. void solve()
  21. {
  22.     int n;
  23.     cin>>n;
  24.     bool prime[n+1];
  25.     memset(prime,true,sizeof(prime));
  26.     vector<ll>cnt(n+1);
  27.     for(int i=2; i<=n; i++)
  28.     {
  29.         if(prime[i])
  30.         {
  31.             for(int k=i+i; k<=n; k+=i)
  32.             {
  33.                 cnt[k]++;
  34.                 prime[k]=false;
  35.             }
  36.         }
  37.     }
  38.     int c=0;
  39.     for(int i=2; i<=n; i++)
  40.     {
  41.         if(cnt[i]==2)
  42.         {
  43.             c++;
  44.         }
  45.     }
  46.     cout<<c<<endl;
  47. }
  48.  
  49. int main()
  50. {
  51.     Kirlos
  52.     ll t;
  53.     t=1;
  54.     //cin>>t;
  55.     while(t--)
  56.     {
  57.         solve();
  58.     }
  59.     return 0;
  60. }
Success #stdin #stdout 0.01s 5516KB
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https://ideone.com/5ShpfK
language:
C++ (gcc 8.3)
created:
2 years ago
visibility:
secret

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