#include<fstream>
using namespace std;
#define MAXN 2000001
ifstream cin("ciur.in");
ofstream cout("ciur.out");
int A[MAXN],N;
int main() {
	int i,j,k=0;
	cin>>N;
	for(i=1;i<=N;i++)
	             A[i]=1;
	for(i=2;i<=N;i++){
		  if(A[i]!=0)
		          {
				   k++;	  			  
		          A[i]=0;			  
	              for(j=i*i;j<=N;j+=i)
		                         A[j]=0;
                   }
    }
	cout<<k;			    				           
	return 0;
}