#include <iostream>

using namespace std;
bool ciur[2000000];
int main()
{
  ifstream cin ("ciur.in");
  ofstream cout ("ciur.out");
    int n, i, prim, j;
    cin >> n;
    for (i = 2; i <= n; i++)
        ciur[i] = true;
    for (i = 2; i <= n; i++)
    {
        if (ciur[i] == true)
          for (j = i * 2; j <= n; j += i)
              ciur[j] = false;
    }
    prim = 0;
    for (i = 2; i <= n; i++)
    {
      if (ciur[i] == true)
        prim++;
    }
    cout << prim;
    return 0;
}