var f,g:text;
    n,i,t,c1,c2,c,l1,l2,j:longint;
    s1,s2,s:string;
begin
     assign(f,'nunta.in');
     assign(g,'nunta.out');
     reset(f);
     rewrite(g);
     read(f,n);
     s1:='1';
     s2:='2';
     s:='';
     for i:=3 to n do
     begin
          t:=0;
          l1:=length(s1);
          l2:=length(s2);
          for j:=1 to l1 do
          begin
               c1:=ord(s1[j])-48;
               c2:=ord(s2[j])-48;
               c:=(c1+c2+t) mod 10;
               t:=(c1+c2+t) div 10;
               s:=s+chr(c+48);
          end;
          if l2>l1 then
          begin
               c2:=ord(s2[l2])-48;
               c:=t+c2;
               s:=s+chr(c+48);
          end;
          if (l1=l2) and (t>0) then
          begin
               s:=s+chr(t+48);
          end;
          s1:=s2;
          s2:=s;
          s:='';
     end;
     if n<4 then write(g,n)
     else
         begin
              if n=1 then write(g,1);
              if n=2 then write(g,2);
              if n=3 then write(g,3);
         end;
     for i:=length(s2) downto 1 do
         write(g,s2[i]);
     close(f);
     close(g);
end.