Here is my program
var
 n,k,i,time:longint;

begin
 readln(n,k);
 if k=1 then writeln(n-1)
  else
   begin
    i:=0;time:=0;n:=n-1;
    while n>0 do
     begin
      if i<k then i:=i+1;
      n:=n-i;time:=time+1;
     end;
    writeln(time);
   end;
end.

> Here is my program
> var
>  n,k,i,time:longint;
>
> begin
>  readln(n,k);
>  if k=1 then writeln(n-1)
>   else
>    begin
>     i:=0;time:=0;n:=n-1;
>     while n>0 do
>      begin
>(***)  if i<k then i:=i+1;
>       n:=n-i;time:=time+1;
>      end;
>     writeln(time);
>    end;
> end.

Have a look at the iteraton..as I understand i is the number of used
cables... But on each iteration you should not add only one cable
(***) but as much as possible, I mean if you have used i cables by
now, next time you could use 2*i cables, if you have so much, NOT
i:=i+1!
Sample input:
12 6
Sample output:
4

1 sec.   1-2
2 sec.   1-3, 2-4
3 sec.   1-5,2-6,3-7,4-8
4 sec.   1-9,2-10,3-11,4-12
Bye!
and Have a luck :)

thanks ...!!!