program ciur;
var p,viz:array[1..100]of integer;
    n,i,j,nr:word;
    f1,f2:text;

begin
assign(f1,'ciur.in'); reset(f1);
assign(f2,'ciur.out'); rewrite(f2);
readln(f1,n);
p[i]:=2;
nr:=1;
i:=1;
repeat  i:=i+2;
  if viz[i]=0 then
     begin
     nr:=nr+1;
     p[nr]:=i;
     j:=i*i;
     while j<=n do
          begin
          viz[j]:=1;
          j:=j+1;
          end;
          end;
          until i>n-2;

writeln(f2,nr);
close(f1);
close(f2);
end.