Write a program with a function 'fun' that takes

an integer as its argument and changes the n-th bit

(counting starting from the right, and with 1)

in its binary-number representation and replaces it

with 1 if it is 0 and with 0 if it is 1, and then

returns the integer with replacements.

For instance, fun(6, 2) should return 4 because

in 6 = 110(2) we replace 1 with 0 to obtain 100.

Similarly, fun(9, 3) = 13 since we replace 9 = 1001(2)

with 1101(2).