Mr. F. wants to get a document be signed by a minister. A minister signs a document only if it is approved by his ministry. The ministry is an M-floor building with floors numbered from 1 to M, 1<=M<=100. Each floor has N rooms (1<=N<=500) also numbered from 1 to N. In each room there is one (and only one) official.
A document is approved by the ministry only if it is signed by at least one official from the M-th floor. An official signs a document only if at least one of the following conditions is satisfied:
a. the official works on the 1st floor;
b. the document is signed by the official working in the room with the same number but situated one floor below;
c. the document is signed by an official working in a neighbouring room (rooms are neighbouring if they are situated on the same floor and their numbers differ by one).
Each official collects a fee for signing a document. The fee is a positive integer not exceeding 10^9.
You should find the cheapest way to approve the document.