#include <iostream>
#include <fstream>
#include <bits/stdc++.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
vector<bool> b;
int main()
{
    int n, i=0, x=2, res=0;
    f>>n;
    b.resize(n, 0);
    while(x<=n)
    {
        res++;
        for(i=x;i<=n;i+=x)b[i]=1;
        while(b[++x]&&x<=n);
    }
    g<<res;
    f.close();
    g.close();
    return 0;
}