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  1. /*
  2.                              uu$$$$$$$$$$$uu
  3.                           uu$$$$$$$$$$$$$$$$$uu
  4.                          u$$$$$$$$$$$$$$$$$$$$$u
  5.                          u$$$$$$$$$$$$$$$$$$$$$$$u
  6.                        u$$$$$$$$$$$$$$$$$$$$$$$$$u
  7.                        u$$$$$$$$$$$$$$$$$$$$$$$$$u
  8.                        u$$$$$$=   =$$$=   =$$$$$$u
  9.                        =$$$$=      u$u       $$$$=
  10.                         $$$u       u$u       u$$$
  11.                         $$$u      u$$$u      u$$$
  12.                          =$$$$uu$$$   $$$uu$$$$=
  13.                           =$$$$$$$=   =$$$$$$$=
  14.                             u$$$$$$$$$$$$$$$u
  15.                              u$=$=$=$=$=$=$u
  16.                   uuu        $$u$ $ $ $ $u$$       uuu
  17.                  u$$$$        $$$$$u$u$u$$$       u$$$$
  18.                   $$$$$uu      =$$$$$$$$$=     uu$$$$$$
  19.                 u$$$$$$$$$$$uu    =====    uuuu$$$$$$$$$
  20.                 $$$$===$$$$$$$$$$uuu   uu$$$$$$$$$===$$$=
  21.                  ===      ==$$$$$$$$$$$uu ==$===
  22.                           uuuu ==$$$$$$$$$$uuu
  23.                  u$$$uuu$$$$$$$$$uu ==$$$$$$$$$$$uuu$$$
  24.                  $$$$$$$$$$====           ==$$$$$$$$$$$=
  25.                    =$$$$$=                      ==$$$$==
  26.                      $$$=                         $$$$=
  27. */
  28. #include <bits/stdc++.h>
  29. using namespace std;
  30. #define Fast                      \
  31.   {                               \
  32.     ios_base::sync_with_stdio(0); \
  33.     cin.tie(0);                   \
  34.     cout.tie(0);                  \
  35.   }
  36. #define ll long long
  37. const int N = 3005;
  38. vector<bool> isPrime(N, true);
  39. void sieve()
  40. {
  41.   isPrime[0] = isPrime[1] = false;
  42.   for (int i = 2; i * i < N; i++)
  43.   {
  44.     if (isPrime[i])
  45.       for (int m = i * i; m < N; m += i)
  46.       {
  47.         isPrime[m] = false;
  48.       }
  49.   }
  50. }
  51. vector<int> divisor(int n)
  52. {
  53.   vector<int> ret;
  54.   for (int i = 1; i * i <= n; i++)
  55.   {
  56.     if (n % i == 0)
  57.     {
  58.       ret.push_back(i);
  59.       if (i * i != n)
  60.         ret.push_back(n / i);
  61.     }
  62.   }
  63.   return ret;
  64. }
  65. void sol()
  66. {
  67.   sieve();
  68.   int n, ans = 0;
  69.   cin >> n;
  70.   for (int i = 1; i <= n; i++)
  71.   {
  72.     int cnt = 0;
  73.     vector<int> a = divisor(i);
  74.     for (int i = 0; i < a.size(); i++)
  75.     {
  76.       if (isPrime[a[i]])
  77.         cnt++;
  78.     }
  79.     if (cnt == 2)
  80.       ans++;
  81.   }
  82.   cout << ans;
  83. }
  84. int32_t main()
  85. {
  86.   Fast;
  87.   int t = 1;
  88.   // cin >> t;
  89.   while (t--)
  90.   {
  91.     sol();
  92.   }
  93. }
Success #stdin #stdout 0.01s 5308KB
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https://ideone.com/QiIh0Y
language:
C++14 (clang 8.0)
created:
6 hours ago
visibility:
public

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