def main():
n, m = map(int, input().split())
t = m % 2 == 1
if t:
n, m = m, n
if m % 2 == 1:
print("-1")
return
ans = []
c = ord('A')
for i in range(n):
ans.append([])
for j in range(m):
ans[i].append(chr(c))
c += j % 2
if t:
n, m = m, n
for i in range(n):
for j in range(m):
print(ans[j][i] if t else ans[i][j], end='')
print()
main()
