#include <fstream.h>
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int v[2000001];
long i,k,n,a;
int main() {
fin>>n;
for (i=2;i<=n;++i)
	if (v[i]==0)
		{
		for (k=2*i;k<=n;k+=i)
			if (v[k]==0)
				v[k]=1;
		a++;
		}
fout<<a;
return 0;
}