#include <cstdio>
#define nMax 2000001

using namespace std;

bool a[nMax];
int n;
int s;

int main()
{
    freopen ("ciur.in", "r", stdin);
    freopen ("ciur.out", "w", stdout);
    scanf ("%d", &n);
    for (int i = 2; i <= n; ++ i){
        if (!a[i]){
            ++ s;
            for (int j = i + i; j <= n; j += i){
                a[j] = 1;
            }
        }
    }
    printf ("%d\n", s);

    return 0;
}