function fib(n: Int64): Int64;

  type TFibMat = array[0..1] of array[0..1] of Int64;
	
  function FibMatMul(a,b: TFibMat): TFibMat;
  var i,j,k: integer;
      tmp: TFibMat;
  begin
    for i := 0 to 1 do
      for j := 0 to 1 do
      begin
	tmp[i,j] := 0;
	for k := 0 to 1 do tmp[i,j] := tmp[i,j] + a[i,k] * b[k,j];
      end;
    FibMatMul := tmp;
  end;
	
  function FibMatExp(a: TFibMat; n: Int64): TFibmat;
  begin
    if n <= 1 then fibmatexp := a
    else if (n mod 2 = 0) then FibMatExp := FibMatExp(FibMatMul(a,a), n div 2)
    else if (n mod 2 = 1) then FibMatExp := FibMatMul(a, FibMatExp(FibMatMul(a,a), n div 2));
  end;

var
  matrix: TFibMat;
	
begin
  matrix[0,0] := 1;
  matrix[0,1] := 1;
  matrix[1,0] := 1;
  matrix[1,1] := 0;
  if n > 1 then
    matrix := fibmatexp(matrix,n-1);
  fib := matrix[0,0];
end;