var
    n: integer;

function fibonachi(n: integer): integer;
begin
    if (n = 1) or (n = 2) then fibonachi := 1
    else fibonachi:= fibonachi(n - 1) + fibonachi(n - 2);
end;

begin
    read(n);
    writeln('F(', n, ') = ', fibonachi(n));
end.

------------------------------------------------------

var
    n, i: integer;
    a: array [1..3] of longint;

begin
    read(n);
    a[2] := 1;
    a[3] := 1;
    for i := 3 to n do
    begin
        a[1] := a[2];
        a[2] := a[3];
        a[3] := a[2] + a[1];
    end;
    writeln('F(', n, ') = ', a[3]);
end.

Verified answer

var
  a1,a2, n, i:integer;
begin

  a1 := 1;

  a2 := 1;
  write('n = '); readln(n);

  for i := 2 to n - 1 do

  begin

    a1 := a1 + a2;

    a2 := a1 - a2;

  end;

  writeln(n, ' элемент последовательности Фибоначчи равен ', a1);

end.