#include <bits/stdc++.h>
using namespace std;
#define ll long long
const ll nmax = 2000005;
char vect[nmax];
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    ll n;
    fin >> n;
    ll cnt = 0;
    for (int i = 2; i <= n; i++)
    {
        if(vect[i] == 0)
        {   cnt++;
            for (int j = i * i; j <= n; j += i)
                vect[j] = 1;
        }
    }

    fout << cnt;
}