#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int v[2000000],nr=1; //pres ca toate nr sunt prime
int main()
{
    int i,j,n;
    cin>>n;
    for(i=3; i<=n; i+=2)
    {
        if(v[i]==0) //daca i e prim
                {nr++;
                    for(j=3; i*j<=n; j++) v[i*j]=1;//eliminam toti multiplii lui
                }
    }
    cout<<nr;
    f.close();
    g.close();
    return 0;
}