Write a function that receives two strings as parameter. This strings are in the following format of date: `YYYY/MM/DD`.
Your job is: Take the `years` and calculate the difference between them.
Examples:
```
'1997/10/10' and '2015/10/10' -> 2015 - 1997 = returns 18 
'2015/10/10' and '1997/10/10' -> 2015 - 1997 = returns 18
```
At this level, you don't need validate months and days to calculate the difference.
def how_many_years (date1, date2):
    get_year = lambda date: int(date.split('/')[0])
    return abs(get_year(date1) - get_year(date2))
def how_many_years (date1, date2):
    get_year = lambda date: int(date.split('/')[0])
    return abs(get_year(date1) - get_year(date2))