Number of Leap Years

Given a range of years as a string, return the number of leap years there are within the range (inclusive).

Examples

num_of_leapyears("1980-1984") ➞ 2
# 1980 and 1984 are leapyears.

num_of_leapyears("2000-2020") ➞ 6

num_of_leapyears("1600-2000") ➞ 98

Notes

• Remember that a hyphen separates the years.