var k,n : longint;  
     f,g : text;  
     p : array[1..2000000] of boolean;  
  
Procedure ciur;  
  var i,j : longint;  
  begin  
  fillchar(p,sizeof(p),true);  
  for i:=2 to n do  
	if p[i] then  
    begin  
		inc(k);  
		j:=2;  
		while i*j<=n do  
		begin  
			p[i*j]:=false;  
			inc(j);  
		end;  
    end;  
 end;  
   
 begin  
 assign(f,'ciur.in');  
 reset(f);  
 readln(f,n);  
 close(f);  
 k:=0;  
 ciur;  
 assign(g,'ciur.out');  
 rewrite(g);  
 writeln(g,k);  
 close(g);  
 end.