This is my program:
program Ural1057;

var
  a,l,r,n,k,ans:longint;
  p:array[0..200]of longint;
  d:array[0..200]of qword;
  num:qword;

procedure dfs(o:longint);

var
  i:longint;

begin
  for i:=p[o-1]+1 to 30 do
    begin
      p[o]:=i;
      num:=num+d[p[o]];
      if num>r then
      begin
        num:=num-d[p[o]];
        exit;
      end;
      if o=n then begin
        if l<=num then inc(ans);
      end else
      dfs(o+1);
      num:=num-d[p[o]];
    end;
end;

begin
  readln(l,r,n,k);
  fillchar(p,sizeof(p),0);
  d[0]:=1;
  a:=1;
  while (d[a-1]<r)and(a<40) do
    begin
      d[a]:=d[a-1]*k;
      inc(a);
    end;
  ans:=0;
  num:=0;
  p[0]:=-1;
  dfs(1);
  writeln(ans);
end.

I don't know why Wa6, who can help me?