input:
10 5
output:
AAAAA AAAAA AAAAA AAAAA AAAAA BBBBB BBBBB BBBBB BBBBB BBBBB
5 10
AAAAABAAAA AAAAACAAAA AAAAABAAAA AAAAACAAAA AAAAABCBCB
4 7
AAAABAA AAAACAA AAAABBC AAAABBA