Problem Description

Zane is the principal of NOI School. The school has $n$ classes, each with $s$ students. The height of the $j$-th student in the $i$-th class is $a_{i,j}$.

Zane wants to select one student from each class to take a photo, such that the difference between the tallest and shortest student among these $n$ students is minimized.

Please output this minimum value.

Input Format

The first line contains two integers $n$ and $s$.

The next $n$ lines each contain $s$ integers, representing the array $a$.

Output Format

Output a single integer representing the answer.

Sample Input and Output

Sample Input #1

2 3
2 1 8
5 4 7

Sample Output #1

1

Sample Input #2

3 3
3 1 4
2 7 18
9 8 10

Sample Output #2

4

Notes

Sample #2 Explanation

Selecting $a_{1,3}, a_{2,2}, a_{3,2}$ results in an answer of $8-4=4$.

Data Range

For $100\%$ of the data, $1 \leq n, s \leq 1000, 1 \leq a_{i,j} \leq 10^9$.

见题面 Input 部分

见题面 Output 部分