You receive queries with the form of
. Find a sequence of size
, formed with
a
's and b
's where you must "find" each query. A query is found if you can find a substring with
a
's and
b
's.
Input Specification
On the first line you will find the number of test cases,
.
For each test case, you will find on the first line and
.
On the next lines, you will find the queries with the space-separated integers
and
.
Output Specification
For each test case, print a sequence which respects the requirement. If you can't find a sequence, print -1
.
Sample Input
1
7 2
4 2
3 3
Sample Output
abaabab
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