#include <fstream.h>
ifstream fin("prim.in");
ofstream fout("prim.out");
long v[2000000],i,k=1,n,j;
int main() {
fin>>k;
for (i=2;i<=2000000;i++)
	if (v[i]==0)
	{ k++;
	for (j=2*i;j<=1350000;j+=i)
		if (v[j]==0)
			v[j]=1;
	}
fout<<k;
return 0;
}