housing has columns year, month and one column per region: south, west, midwest, northeast.

Return a Series indexed by year giving the total units completed across all four regions in that year, sorted by year.

Input

   year  month  south  west  midwest  northeast
0  2020      1     10     1        5          0
1  2020      2     20     2        5          1
2  2021      1     30     3        5          2

Output

year
2020    44
2021    40
dtype: int64