program calcfib (input, output);

var n : integer;
   
function fib (n: integer) : integer;
var a, b, t, i : integer;
begin
   a := 1;
   b := 1;
   for i := 2 to n do
   begin
      t := a + b;
      a := b;
      b := t
   end;
   fib := b
end;

begin
   readln(n);
   writeln(fib(n))
end.