a,b=map(int,input().split())

if len(str(a))!=len(str(b)):
    print(max(a,b))
else:
    for i,j in zip(str(a),str(b)):
        c,d=int(i),int(j)
        if c==4 and d==7:
            print(a)
            break
        elif c==7 and d==4:
            print(b)
            break
        elif c>d:
            print(a)
            break
        elif d>c:
            print(b)
            break