program pr1;

{$APPTYPE CONSOLE}

uses
  math;

var n:integer;
f:real;
begin
readln (n);
//n:=n+1;
f:=1/sqrt(5)*(power((1+sqrt(5))/2,n)+power((1-sqrt(5))/2,n));
writeln(f:0:0);
readln;
  { TODO -oUser -cConsole Main : Insert code here }
end.