#include <bits/stdc++.h>

using namespace std;
bitset<2000000>a;
ifstream in("ciur.in");
ofstream out("ciur.out");
void Ciur(int n)
{
   int i, j;
    a[1]=1;
    for(i = 4; i <= n; i += 2)a[i] = 1;
     for(i = 3; i * i <=n; i = i + 2)
      if(a[i] == 0)
       for(j = i * i; j <= n; j = j + 2 * i)a[j] = 1;

}

int main()
{
    int n, i, nr = 0;
    in >> n;
    Ciur(n);
    for (i = 2; i <= n; i++)
      if(a[i] == 0)nr++;
      out << nr << "\n";
    in.close();
    out.close();
    return 0;
}