#include <fstream>
#include <cmath>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int N;
int v[2000001];
int nr = 0;

int main()
{

    fin >> N;

    for (int i = 2; i <= N; i++)
        v[i] = 0;

    for (int i = 2; i <= N; i++)
        if (v[i] == 0) {
            nr++;
            for (int j = 2 * i; j <= N; j = j + i)
                v[j] = 1;
        }


    fout << nr;

    return 0;
}