Problem Description

Given a rectangular matrix, calculate the sum of all elements on the border (first row, last row, first column, last column). Count corner elements only once.

Input Format

First line contains m and n (matrix dimensions). Next m lines contain n space-separated integers each.

Output Format

A single integer representing the sum of border elements.

Constraints

• 1 ≤ m, n ≤ 100

• -1000 ≤ matrix elements ≤ 1000

• For 1x1 matrix, the single element is the border

• Corner elements counted only once

Sample Input/Output

3 4
1 2 3 4
5 6 7 8
9 10 11 12

54

Explanation

Border elements are: Top row: 1+2+3+4=10, Bottom row: 9+10+11+12=42, Left column (excluding corners): 5, Right column (excluding corners): 8. Total: 10+42+5+8-4=54. We subtract 4 because corners were counted twice.