begin
   comment LIBRARY 1;
   integer
     NN;
   switch A ≔      B[1],
     B[2];
   switch B ≔      A[G],
     A[2];
   integerprocedure F(N, S);
      value
        N;
      integer
        N;
        switch
        S;
   begin
      NN ≔ N;
      goto S[1];
      F ≔ NN
   end;
   integerprocedure G;
   begin
      integer
        N;
      N ≔ NN;
      G ≔ 0;
      NN ≔         if N ⩽ 1 then
        N
      else
        F(N - 1, A) + F(N - 2, A)
   end;
   OUTREAL(99, F(20, A))
end