#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int nr, n;
bool p[400005];


int prim2()
{
    for (int i = 3; i <= n; i += 2) {
      if (p[i] == 0) {
        nr++;
        for (int j = i + i + i; j <= n; j += i * 2 ){
          p[j] = 1;
        }
      }
    }
    return nr+1;
}
int main()
{
    fin >> n;
    fout<<prim2();

}