#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool p[2000005];
int n;
int main()
{
    in>>n;
    int i, j, nr = 1;
    for (i = 3;i*i<= n;i+=2) {
      if (p[i] == 0) {
        for (j = i*i; j <= n; j +=2*i) {
          p[j] = 1;
        }
      }
    }
    for (i=3; i<= n; i+=2)
        if (p[i] == 0) nr++;
    out<<nr;
    return 0;
}