You receive some random elements as a space-delimited string. Check if the elements are part of an ascending sequence of integers starting with 1, with an increment of 1 (e.g. 1, 2, 3, 4).
Return:
* `0` if the elements can form such a sequence, and no number is missing ("not broken", e.g. `"1 2 4 3"`)
* `1` if there are any non-numeric elements in the input ("invalid", e.g. `"1 2 a"`)
* `n` if the elements are part of such a sequence, but some numbers are missing, and `n` is the lowest of them ("broken", e.g. `"1 2 4"` or `"1 5"`)
## Examples
```
"1 2 3 4"  ==>  return 0, because the sequence is complete
"1 2 4 3"  ==>  return 0, because the sequence is complete (order doesn't matter)
"2 1 3 a"  ==>  return 1, because it contains a non numerical character
"1 3 2 5"  ==>  return 4, because 4 is missing from the sequence
"1 5"      ==>  return 2, because the sequence is missing 2, 3, 4 and 2 is the lowest
```
def find_missing_number(sequence):
    if not sequence:
        return 0
    try:
        l = [int(elem) for elem in sequence.split(' ')]
    except ValueError:
        return 1
    for i in range(1, len(l)+1):
        if i not in l:
            return i
    return 0
def find_missing_number(sequence):
    if not sequence:
        return 0
    try:
        l = [int(elem) for elem in sequence.split(' ')]
    except ValueError:
        return 1
    for i in range(1, len(l)+1):
        if i not in l:
            return i
    return 0