#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out( "ciur.out");
int n,k,V[2000001],t=0;
int main()
{


    in>>n;
    for (int i=2;i<=n;i++)
    {
        if(V[i]==0)
        {
            k=1;
            t++;
            while(k*i<=n)
                V[(k++)*i]=1;
        }
    }
    out<<t;
    return 0;
}