#include <stdio.h>

using namespace std;

int cnt, N;
char prim[2000005];


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

    scanf ("%d", &N);
    for (d=2; d<=N; d++)
        prim[d]=1;
    for (d=2; d<=N; d++)
        if (prim[d])
    {
        cnt++;
        for (i=d+d; i<=N; i+=d)
                prim [i]=0;
    }


    printf ("%d", cnt);

    return 0;
}