program ciur;
type vector=array [1..20000] of boolean;
var v:vector;
    n,i,j,x: longint;
begin
  assign(input,'ciur.in'); reset(input);
  assign(output,'ciur.out'); rewrite(output);
     readln(n);
  for i := 1 to N do
      v[i]:= true;

  for i := 2 to n do
      if v[i] then
      for j := 2 to n div i do
        v[i*j] := false;

  x:= 0;
  for i := 2 to n do
    if v[i] then
       x:=x+1;
  write(x);

close(input); close(output);
end.