// the Sieve of Eratosthenes
#include <bits/stdc++.h>
using namespace std;

signed main()
{
  int n;
  cin >> n;
  vector<bool> NotPrime(n + 10);
  vector<int> Prime(n + 10);
  int tot = 0;
  function<void(int)> EratoSieve = [&](int n)
  {
    for (int i = 2; i <= n; i ++)
    {
      if (!NotPrime[i]) 
      {
        Prime[tot ++] = i;
        for (int j = i + i; j <= n; j += i) NotPrime[j] = true;
      }
    }
  };
  EratoSieve(n);
  cout << tot << "\n";
  return 0;
}

// the Sieve of Euler
#include <bits/stdc++.h>
using namespace std;
signed main()
{
  int n; 
  cin >> n;
  int tot = 0;
  vector<int> Prime(n + 10);
  vector<bool> NotPrime(n + 10);
  function<void(int)> EulerSieve = [&](int n)
  {
    for (int i = 2; i <= n; i ++)
    {
      if (!NotPrime[i]) Prime[tot ++] = i;
      for (int j = 0; Prime[j] <= n / i; j ++)
      {
        NotPrime[i * Prime[j]] = true;
        if (i % Prime[j] == 0) break;
      }
    }
  };
  EulerSieve(n);
  cout << tot << "\n";
  return 0;
}
/*
筛法中若要数组Prime从1开始，需要++total，并且后续筛法中的j需要从1开始
否则则为0 -> total++ -> j from 0 to n
*/