#include <iostream>
#include <fstream>
using namespace std;

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

    char v[2000000];
int main()
{
    int x,nr=0;
    fin>>x;
    for (int i=2;i<=x;i++)
        v[i]=0;
    for (int i=2;i<=x;i++) {
        if (v[i]==0) nr++;
        int j=2;
        while (i*j<=x) {
            v[i*j]=1;
            j++;
        }
    }
    fout<<nr;
    return 0;
}