#include <cstdio>

using namespace std;

int n, sol;
int prim[2000005];
int i, j;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf ("%d", &n);
    for (i=2; i<=n; ++i) {
        if (!prim[i]) {
            sol++;
            for (j=i+i; j<=n; j+=i)
                prim[j] = 1;
        }
    }
    printf ("%d", sol);
    return 0;
}