Given a string of ‘a’ and ‘b’ only

for example

string is ‘baaab’ and x=3 and y=3

Find the lexicographical smallest permutation of string that contains

count of sub-sequence ‘ab’ = x times and count of sub-sequence ‘ba’ = y times.

For above example , there is a possible permutation **ababa**

We can print -1 , in case if its not possible

for example when string is ‘abbb’ and x = 3 and y = 3.

For this example no permutation is possible

What logic will you use ?