participant, the United States shall be entitled to recover from the participant an amount determined in accordance with the following formula: A = 3Φ(t − s/t). (B) Formula variables In the formula specified in subparagraph (A): (i) A is the amount the United States is entitled to recover from the participant. (ii) Φ is the sum of— (I) the amounts paid under this section to or on behalf of the participant