#include <fstream>
#include <math.h>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int main()
{
    int a[1001];
    int nr = 0, n, i, j;
    f>>n;
    for (i = 2; i <= n; i++)
        a[i] = 1;
    for (i = 2; i <= sqrt(n); i++)
        if (a[i] != 0)
            for (j = 2; j <= n / i; j++)
                a[i*j] = 0;
    for (i = 2; i <= n; i++)
        if (a[i] != 0)
            nr++;
    g<< nr << endl;
    return 0;
}