I have DataFrame in Python Pandas like below:
Data types:

• MONTH_NR - numeric
• MONTH_NAME - object
• VALUE - numeric

And I need to add 3 new ROWS where will be:

1. sum of values from column "VALUE" after 6 month (from 1 till 6)
2. sum of values from column "VALUE" after 12 month (from 7 till 12)
3. sum of values from column "VALUE" after 12 month (from 1 till 12)
   So as a result I need somethin like below:

MONTH_NR | MONTH_NAME  | VALUE
    ---------|-------------|---------
    1        | JANUARY     |  10
    2        | FEBRYARY    |  20
    3        | MARCH       |  15
    4        | APRIL       |  10
    5        | MAY         |  11
    6        | JUN         |  100
SUM_AFTER_1_6|             |  166
    7        | JULY        |  200
    8        | AUGUST      |  12
    9        | SEPTEMBER   |  20
    10       | OCTOBER     |  50
    11       | NOVEMBER    |  30
    12       | DECEMBER    |  50
SUM_AFTER_7_12|             |  362
SUM_ALL      |             |  528

How can I do that in Python Pandas ?