A medical representative visited the doctors P, Q, R, S, T and U from Monday to Saturday - only one doctor per day.

i. He visited U on some day before visiting R and T.
ii. He visited P on the previous day of visiting S, but not on Thursday.
iii. He did not visit either Q or S on the last day.
iv. He visited Q just after U, but not on Tuesday.

Which are the two doctors he visited on the first two days?