Complete the function that takes an array of words.
You must concatenate the `n`th letter from each word to construct a new word which should be returned as a string, where `n` is the position of the word in the list.
For example:
```
["yoda", "best", "has"]  -->  "yes"
  ^        ^        ^
  n=0     n=1     n=2
```
**Note:** Test cases contain valid input only - i.e. a string array or an empty array; and each word will have enough letters.
nth_char = lambda w:''.join(x[i] for i,x in enumerate(w))

nth_char = lambda w:''.join(x[i] for i,x in enumerate(w))
