you can look

var
a1,a0,p:extended;
n,k,i:extended;
begin
readln(n,k);
a1:=k-1;
i:=1;
{for i:=2 to n do
begin }
repeat
i:=i+1;
p:=a1;
a1:=(a1+a0)*(k-1);
a0:=p;
until i>=n;
{end; }
writeln(a1+a0:0:0);
end.

You way are currect but you MUST use HI-precision