The following incomplete (columns have missing amounts) pension spreadsheet is for Old Tucson Corporation (OTC).

($ in millions) Debit(Credit)	PBO	Plan Assets	Prior Service Cost	Net (Gain)Loss	Pension Expense	Cash	Net Pension (Liability)/Asset
Beginning balance	(610)			91
Service cost					95
Interest cost
Expected return on assets					(34)
Gain/loss on assets				(4)
Amortization of:
Prior service cost			(17)
Net gain/loss
Loss on PBO	(36)			36
Contributions to fund						(34)
Retiree benefits paid	65	(65)
Ending balance	(702)	352	87	111			(350)

What was the prior service cost at the beginning of the year?