#include <iostream>
#include <fstream>
#include <cmath>
#include <bitset>
using namespace std;

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

const int NMAX = 2000005;

bitset<NMAX> p;

int main()
{
    int n, i, j, r;

    fin>>n;

    p[1] = 1;
    r = sqrt(n) + 1;

    int prime = 0;
    for(i=3; i<r; i+=2)
    {
        if(!p[i])
        {
            prime++;
            for(j=i*i; j<=n; j+=(2*i))
            {
                p[i] = 1;
            }
        }
    }

    r+=(r%2==0);

    for(i=r; i<=n; i+=2)
    {
        if(!p[i])
        {
            prime++;
        }
    }

    fout<<prime;
}