you have a box full of some tiles . All tiles have some character from a-z or is blank.

There are n numbers of tiles.
You have to select 7 tiles randomly from the box.
Count the number of different possible combinations you can pick from the bag. You have to return just the count.
Suppose the tiles in the bag are given as a map like below:
a - 3
b- 2
c- 3
.
.
.
blank - 4

Order of tiles do not matter.

Example:
following are some valid combinations:

abbcc_ _ = _ _ ccbba
a_ _ _ _ bb
aaabbcc
and so on

if a is added once, decrement counter of a by 1.