#include <iostream>
#include <fstream>
#include <algorithm>
#include <stdio.h>
#include <string>
#include <math.h>
#include <vector>
#define lm 2000001
#define pb push_back

using namespace std;

int n,res=0;
bool l[lm];

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>n;
    for (int i=2; i<=n; i++)
        if(!l[i])
        {
            res++;
            for (int j=i+i; j<=n; j+=i)
                l[j]=true;
        }
    g<<res;

 return 0;
}