#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    int j,n,nr=1;
    ifstream f("ciur.in");
    f>>n;
    char v[n+1];
    for (int i=2;i<=n;i++) v[i]=0;
    j=3;
    while (j<=n)
    {
        nr++;
        for (int i=j;i<=n;i=i+i) v[i]=1;
        while (v[j]==1) j+=2;
    }
    ofstream g("ciur.out");
    g<<nr;
    return 0;
}