1099 B basis is not reported to IRS and is blank

I have a 1099 B with long-term basis not reported to IRS.   Do I simply report my known basis in the second box 'Total cost or other basis (sum of all Box 1e), even though it's blank on the 1099 B?  Or do I enter $0, then select I need to adjust my cost basis and then check 'B' cost basis incorrect on form?