slice sender_address = cs~load_msg_addr();
  cs~load_msg_addr(); ;; skip dst
  cs~load_coins(); ;; skip value
  cs~skip_bits(1); ;; skip extracurrency collection
  cs~load_coins(); ;; skip ihr_fee
  int fwd_fee = muldiv(cs~load_coins(), 3, 2); ;; we use message fwd_fee for estimation of forward_payload costs

  int op = in_msg_body~load_uint(32);