#include <fstream>
#define nmax 2000000+5
using namespace std;

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

bool ePrim[nmax];
int n;
int cnt;

int main()
{
    int i, j;

    fin >> n;

    for (i = 2; i <= n; i++)
        ePrim[i] = 1;

    for (i = 2; i <= n; i++)
        if (ePrim[i])
        {
            cnt++;
            for (j = i * 2; j <= n; j += i)
                ePrim[j] = 0;
        }

    fout << cnt << '\n';
    return 0;
}