#include <iostream>
#include <fstream>

using namespace std;

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

bool vec[2000005];

int main()
{
    int numar;
    long long nr_prime=1;
    in >> numar;
    for(int i=3; i<=numar; i+=2)
        if(vec[i]==0)
        {
            nr_prime++;
            for(int j=i+i+i; j<=numar; j+=i+i)
                vec[j]=1;
        }
    out << nr_prime;
    return 0;
}