This is my code:

{$N+}
program u1066;

 var
   n,i:longint;
   a1,an,tmp:extended;

begin
  readln(n,a1);
  for i:=3 to n do
  begin
    tmp:=(a1-i+1)*(i-2)/(i-1);
    if tmp>an then an:=tmp;
  end;
  an:=(n-1)*an+(n-1)*(n-2)-(n-2)*a1;
  if an<0 then an:=0;
  writeln(an:0:2);
end.

I tried these:
100 100 =>7921.00
10 11 =>32.00
123 456 =>10128.86
111 111 =>9891.00
8 15 =>9.75
5 10 =>0.67
70 50 =>3835.14
1000 1=>996004.00