#include<fstream>
#include<cstdlib>
#define MAXN 2000010
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
long n,i,j,nr,v[MAXN];
int main ()
{
	f>>n;
	v[0]=1;
	v[1]=1;
	i=3;
	nr=1;
	while(i<=n)
		{
			while(v[i]==1&&i<=n)
				i+=2;
			if(i<=n)
				nr++;
			j=i*i;
			while(j<=n)
				{
					v[j]=1;
					j+=i;
				}
			i+=2;
		}
	g<<nr<<'\n';
	f.close();
	g.close();
	return 0;
}