#include <cstdio>
using namespace std;
int n, sol;
char prim[2000001];
int main()
{
    int i, j;

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

    scanf ("%d", &n);
    sol++;
    for (i=3; i<=n; i+=2) {
        if (prim[i] == 0) {
            sol++;
            for (j=i+i; j<=n; j+=i)
                prim[j] = 1;
        }
    }
    printf ("%d", sol);
    return 0;
}