#968. Longest common prefix
You get n words. Print the longest prefix that all of them share. If there is none, print `None`.
### Input
n, then n lines with a word.
### Output
One line.
Examples
Input
3 yz vaq variayz
Output
None
Input
3 ryz robotyz robotx
Output
r
💡 You can solve it with Python, JavaScript or blocks. Read the input line by line with input(). Don't print a question (like input("Number: ")). Print exactly what the output asks for, nothing more.