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

ifstream cin("ciur.in");
ofstream cout("ciur.out");

constexpr int NMAX = 2e6 + 1;

bitset<NMAX> eratostene;

int main()
{
    eratostene[1] = 1;
    int n,ans = 0; cin >> n;
    for(int i = 2; i * i <= n ; i++)
        {
            if(eratostene[i]) continue;
            ans++ ; for(int j = 2 * i ; j <= n ; j += i) eratostene[j] = 1;
        }

    cout << ans;
}