#include<fstream.h>

ifstream f("ciur.in");
ofstream g("ciur.out");
long n,i,j,k=0;
char a[2000005];
int main ()
{
	f>>n;
	for (i=2; i<=n; i++)
		a[i]=1;
	for (i=2; i<=n; i++)
		if(a[i]==1)
		{
			k++;
			for (j=i+i; j<=n; j+=i)
				a[j]=0;
		}
        g<<k;
	return 0;
}