#include<fstream>
using namespace std;
int N, cnt;    
  char prim[2000005]; 
int main(void)
{
  int i,j;
  ifstream f ("ciur.in");
  ofstream g ("ciur.out");
  f>>N;
for (i=2;i<=N;i++)
prim[i]=1;
for (i=2;i<=N;i++)
if (prim[i])
{
            cnt++;
            for (j=i+i;j<= N; j=j+i)
            prim [j]=0;
            }
            g<<cnt;
            
            return 0;  
    
}