The post office is right in front of the bank, you know.

Literal

Post-office [topic-は] bank-of exactly direct-front is-[plain-だよ].

真ん前 ('directly in front, right in front of') uses the intensifier 真ん- (variant of 真っ-) to emphasize the directness. ちょうど ('exactly, precisely') doubles down on the exactness. A casual, helpful direction.