Your task in order to complete this Kata is to write a function which formats a duration, given as a number of seconds, in a human-friendly way.
The function must accept a non-negative integer. If it is zero, it just returns `"now"`. Otherwise,  the duration is expressed as a combination of `years`, `days`, `hours`, `minutes` and `seconds`.
It is much easier to understand with an example:
```Fortran
formatDuration (62)    // returns "1 minute and 2 seconds"
formatDuration (3662)  // returns "1 hour, 1 minute and 2 seconds"
```
```python
format_duration(62)    # returns "1 minute and 2 seconds"
format_duration(3662)  # returns "1 hour, 1 minute and 2 seconds"
```
**For the purpose of this Kata, a year is 365 days and a day is 24 hours.**
Note that spaces are important.
### Detailed rules
The resulting expression is made of components like `4 seconds`, `1 year`, etc.  In general, a positive integer and one of the valid units of time, separated by a space. The unit of time is used in plural if the integer is greater than 1.
The components are separated by a comma and a space (`", "`). Except the last component, which is separated by `" and "`, just like it would be written in English. 
A more significant units of time will occur before than a least significant one. Therefore, `1 second and 1 year` is not correct, but `1 year and 1 second` is.
Different components have different unit of times. So there is not repeated units like in `5 seconds and 1 second`.
A component will not appear at all if its value happens to be zero.  Hence, `1 minute and 0 seconds` is not valid, but it should be just `1 minute`.
 A unit of time must be used "as much as possible". It means that the function should not return `61 seconds`, but `1 minute and 1 second` instead.  Formally, the duration specified by  of a component must not be greater than any valid more significant unit of time.
def format_duration(s):
    dt = []
    for b, w in [(60, 'second'), (60, 'minute'), (24, 'hour'), (365, 'day'), (s+1, 'year')]:
        s, m = divmod(s, b)
        if m: dt.append('%d %s%s' % (m, w, 's' * (m > 1)))
    return ' and '.join(', '.join(dt[::-1]).rsplit(', ', 1)) or 'now'
def format_duration(s):
    dt = []
    for b, w in [(60, 'second'), (60, 'minute'), (24, 'hour'), (365, 'day'), (s+1, 'year')]:
        s, m = divmod(s, b)
        if m: dt.append('%d %s%s' % (m, w, 's' * (m > 1)))
    return ' and '.join(', '.join(dt[::-1]).rsplit(', ', 1)) or 'now'