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

#define MAX 2000001
ifstream cin ("ciur.in");
ofstream cout ("ciur.out");

bitset <MAX> ciur;
int n;

int main()
{
    cin >> n;

    ciur[0] = 0;
    ciur[1] = 1;

    for (int i = 2; i * i <= n; i++)
    {
        if (!ciur[i])
        {
            for (int j = i * i; j <= n; j += i)
            {
                ciur[j] = 1;
            }
        }
    }


    int cnt = 0;
    for (int i = 2; i <= n; i++)
    {
        if (!ciur[i])
        {
            cnt++;
        }
    }

    cout << cnt << "\n";
    return 0;
}