#include<iostream>
#include<fstream.h>
char v[2000001]={0};long i,k,j,n;
int main()
{
ifstream fin("ciur.in");
ofstream fout("ciur.out");
	
fin>>n;

for(i=2;i<=n;i++)
if(v[i]==0)
{
  k++;
   for(j=2;j<=n/i;j++)
  v[i*j]=1;
}
fout<<k;
fin.close();
fout.close();
return 0;}