#include <stdlib.h>
#include <math.h>
#include <stdio.h>
int main()
{
    int *a,n,l=0;
    freopen("ciur.in" , "rt", stdin);
    freopen("ciur.out", "wt", stdout);

    scanf("%d", &n);
    a = (int *) malloc((n+1)*sizeof(int));
    for (int i=2;i<=n;i++)
        a[i]=1;
    for (int i=2;i<=sqrt(n);i++)
        if (a[i])
            for (int j=i;j<=n/i;j++)
     a[i*j]=0;
        for (int i=2;i<=n;i++)
            if (a[i]) l++;

    printf("%d", l);

    return 0;

}