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