# include <iostream>
# include <fstream>
# include <bitset>
using namespace std;

# define MAXN 2000003

ifstream f("ciur.in");
ofstream g("ciur.out");

bitset<MAXN> prim;

int main()
{
    int n, s = 0;
    f >> n;

    prim.set();
    for (int i = 2; i <= n; i++) {
        if (prim[i] == true) {
            s++;
            for (int j = i + i; j <= n; j += i) {
                prim[j] = false;
            }
        }
    }

    g << s;

    return 0;
}