def find_min_digits(l, r):
    min_digits = float('inf')
    for i in range(10 ** (r - l + 1)):
        num_str = str(i).zfill(r - l)
        if all(num_str[j] != num_str[j + 1] for j in range(len(num_str) - 1)):
            min_digits = min(min_digits, int(num_str))
    return min_digits if min_digits != float('inf') else -1

T = int(input())
for _ in range(T):
    l, r = map(int, input().split())
    result = find_min_digits(l, r)
    print(result)