import collections,sys,math,functools,operator,itertools,bisect,heapq,decimal,string,time,random
#sys.setrecursionlimit(10**9)
#sys.set_int_max_str_digits(0)
#input = sys.stdin.readline
n = int(input())
s = int(input())
ans = []
a = 'ABC'
for i in itertools.product([0,1,2],repeat=n):
    cnt = [0,0,0]
    t = []
    for j in range(n):
        cnt[i[j]] += 1
        t.append(a[i[j]])
    if all(cnt[j] >= 1 for j in range(3)):
        ans.append(''.join(t))
ans.sort()
if s-1 < len(ans):
    print(ans[s-1])
else:
    exit(print(-1))