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

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

int ciur(int n)
{
    vector<bool> prime(n+1,true);
    int primeNumbers = 0;
    for(int i=2; i<=n; i++)
    {
        if(prime[i]==false)
            continue;
        int currentIndex = 1;
        primeNumbers++;
        while(currentIndex*i <= n)
        {
            prime[currentIndex*i] = false;
            currentIndex++;
        }
    }
    return primeNumbers;
}


int main()
{
    int n;
    fin>>n;
    fout<< ciur(n);

    return 0;
}