#include <iostream>
#include <fstream>
#include <algorithm>
#include <cstring>
#include <vector>
#include <bitset>
#include <cmath>
#define x first
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int N, sol=1;
bitset < 2000005 > prim;

int main()
{
    f>>N;

    for (int i=4; i<=N; i+=2)
        prim[i]=1;

    for (int i=3; i<=N; i+=2)
        if (!prim[i])
        {
            ++sol;
            for (int j=i; j<=N; j+=i)
                prim[j]=1;
        }

    g<<sol<<'\n';
    return 0;
}