#include <stdio.h>

int i,n,j,count;
int v[2000100];

int main ()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);
    
    scanf ("%d",&n);
    
    for (i=2;i<=n;i++)
        if (v[i]==0) {
                     for (j=i*i;j<=n;j=j+i) v[j]=1;
                     count++;
                     }
    
    //for (i=2;i<=n;i++) if (v[i]==0) count++;
                   
    printf ("%d",count);
    
    return 0;
}