a,b = raw_input().split()
if len(a) > len(b):
    print a
elif len(a) < len(b):
    print b
else:
    for c,d in zip(a,b):
        if c == d:
            continue
        elif c == '4' and d == '7':
            print a
            break
        elif c == '7' and d == '4':
            print b
            break
        else:
            print a if c > d else b
            break