var f:text;
    i,N:integer;
    c,a,b:string;
Procedure adun(var c:string;b,a:string);
var i,t:byte;
    x:integer;
begin
     for i:=1 to length(b)-length(a) do
         a:='0'+a;
     t:=0;
     c:='';
     for i:=length(a) downto 1 do
         begin
              x:=(ord(a[i])-48)+(ord(b[i])-48)+t;
              t:=x Div 10;
              c:=Chr(x Mod 10+48)+c;
         end;
     if t<>0 then c:=Chr(t+48)+c;
end;
Begin
     assign(f,'nunta.in'); reset(f);
     Readln(f,N);
     close(f);
     assign(f,'nunta.out'); rewrite(f);
     if N=1 then write(f,'1')
        else if N=2 then write (f,'2')
           else begin
                     a:='1'; b:='2';
                     for i:=2 to N do
                     begin
                          adun(c,b,a);
                          a:=b;
                          b:=c;
                     end;
                     writeln(f,c);
              end;
     close(f);
End.