Island Perimeter (Round 3, LC 463 :)

0 is water and 1 is land. Land cells connected 4-directionally form exactly one island with no lakes, surrounded by water. Each cell has side length 1. Find the perimeter of the island.

输入格式

The first line contains N M (1..100), followed by N lines each with M values 0/1. There is guaranteed to be exactly one island and no inner lakes.

输出格式

Output a single integer, the answer.

样例 1

输入：

1 1
1

输出：

4

样例 2

输入：

2 2
1 1
1 1

输出：

8

样例 3

输入：

2 2
1 0
1 1

输出：

8

样例说明

Example 1: a single cell has four sides, so the perimeter is 4.

Example 2: a solid 2×2 square has sides of length 2, so the perimeter is 8.

Example 3: three cells contribute 12, minus 4 for the two shared edges, giving a perimeter of 8.