var
  a : array [1..1000] of longint;
  i,n : longint;
begin
  readln(n);
  a[1]:=1;
  a[2]:=1;
  i:=3;
  for i:=3 to n do
    a[i]:=a[i-1]+a[i-2];
  writeln(a[n]);
end.