Description

Input an integer matrix and calculate the sum of elements located on the edges of the matrix. The edge elements are those in the first and last rows, as well as the first and last columns.

Input Format

The first line contains two integers m and n (m < 100, n < 100), representing the number of rows and columns of the matrix, separated by a space.
The next m lines each contain n integers (ranging from 0 to 9), separated by spaces.

Output Format

Output the sum of the edge elements of the matrix.

Sample

3 3
3 4 1
3 7 1
2 0 1

15