#include<cstdio>
#include<algorithm>
using namespace std;
bool v[2000002];
int i,j,x,n;
int main ()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);
    scanf ("%d",&n);x=1;
   for(i=3;i*i<=n;i+=2)
		if(!v[i])
			for(j=i*i;j<=n;j+=i+i) v[j]=1;
    for (i=3;i<=n;i+=2) {if (v[i]==false) ++x;}
    printf ("%d",x);
    return 0;
}