//#include <iostream>
#include <bits/stdc++.h>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int Max=2000005;
bool viz[Max]; int n,nr;
int main()
{
    in>>n;
    for(int i=3;i<=n;i+=2)
    {
        if(!viz[i])
        {
            nr++;
            for(int d=3*i;d<=n;d+=2*i)
            viz[d]=1;
        }

    }

    if(n>=2) nr++;
    out<<nr;
    return 0;
}