#include <iostream>
#include <fstream>
#define nmax 2000005
using namespace std;

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

bool c[nmax];
int n;
int main()
{
    int i,j,ct;
    fin>>n;
    c[2]=true;
    for(i=3;i<=n;i=i+2)
    c[i]=true;
    for(i=3;i*i<=n;i++)
    if(c[i]==true)
         for(j=3*i;j<=n;j=j+2*i)
             c[j]=false;
    ct=1;
    for(i=3;i<=n;i++)
    if(c[i]==true)
        ct++;
    fout<<ct;
    return 0;
}