#include <iostream>
#include<fstream>
#define N 2000005
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool c[N];
int n;


void ciur()
{
    int i,j;
    c[2]=1;
    for(i=3;i<=n;i=i+2)c[i]=1;
    for(i=3;i*i<=n;i=i+2)
        if(c[i])
        for(j=3*i;j<=n;j=j+2*i)
            c[j]=0;

}


int main()
{
    int i,ct=0;
    fin>>n;
    ciur();
    for(i=1;i<=n;++i)
        if(c[i])ct++;
    fout<<ct;

    return 0;
}