var n,i,k,a:longint;
    ok:boolean;
    v:array[1..5000] of longint;
    f,g:text;
begin
assign(f,'ciur.in');reset(f);
readln(f,n);close(f);
assign(g,'ciur.out');rewrite(g);
if n=2 then writeln(g,1)
       else if n in [3,4] then writeln(g,2)
       else begin
v[1]:=2;v[2]:=3;v[3]:=5;
k:=3;
for a:=7 to n do
 begin
  ok:=true;
  i:=0;
  repeat
   i:=i+1;
   if a mod v[i]=0 then ok:=false;
  until (not ok) or (i=k);
  if ok then begin k:=k+1;
                   v[k]:=a;
             end;
 end;
writeln(g,k);
end;
close(g);
end.