type vect= array [1..100] of integer;
 var v:vect; n,i,j,nr:integer;   f,g:text;
  begin
  assign(f,'ciur.in');reset(f);
  assign(g,'ciur.out');rewrite(g);
  read(f,n);
   for i:= 2 to n do
    v[i]:=i;
     nr:=0;
     for i:=2 to n do
      if v[i]<>0 then
        for j:=2 to n div i do
         v[i*j]:=0;
   { while i<=n do
     begin
      j:=i;
         while j<=n do
         begin
             j:=j+i;
             v[j]:=0;end;
             inc(i);
           end;      }
         for i:=1 to n do
         if v[i]<>0 then inc(nr);
       write(g,nr);
       close(g);
       end.