#include <fstream>

using namespace std;

const int DIM = 2000001;

bool c[DIM];
int n, nr;

int main () {

    FILE *f = fopen ("ciur.in", "r");
    FILE *g = fopen ("ciur.out", "w");

    int i, j;

    fscanf (f, "%d", &n);

    for (i = 2; i <= n; ++i)
        if (!c[i])
            for (j = 2 * i; j <= n; j += i)
                c[j] = 1;

    for (i = 2; i <= n; ++i)
        if (!c[i])
            ++nr;

    fprintf (g, "%d", nr);

    fclose (f);
    fclose (g);

    return 0;
}