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

ifstream cin("ciur.in");
ofstream cout("ciur.out");

#define MAXSIZE 2000005

bool c[MAXSIZE];
int N;
int nr_prime = 1;

void ciur()
{
    for(int i = 4; i <= N; i+=2)
        c[i] = true;
    for(int i = 3; i <= N; i+=2)
        if(!c[i])
        {
            ++nr_prime;
            for(int j = 3*i; j <= N; j+=(i<<1))
                 c[j] = true;
        }
}


int main()
{
   cin>>N;
   ciur();
   cout<<nr_prime;
}