#include <iostream>
#include <stdio.h>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream out("ciur.out");
int N,ct;
char prim[2000005];
int main(void)
{
    int i,j;
    fin>>N;
    for(i=2;i<=N;++i)
        prim[i]=1;
    for(i=2;i<=N;++i)
    {
        if(prim[i])
        {
            ++ct;
            for(j=i+i;j<=N;j+=i)
                prim[j]=0;
        }
    }
    out<<ct;
    fin.close();
    out.close();
    return 0;
}