#include <stdio.h>

using namespace std;

int cnt, N, d, i;
char prim[2000005];


int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf ("%d", &N);

    for (d=2; d<=N; d++)
        prim[d]=0;

    for (d=2; d*d<=N; d++)
        if (prim[d])
    {
        cnt++;
            for (i=d*d; i<=N; i+=d)
                prim [i]=0;
    }

    printf ("%d", &cnt);

    return 0;
}