A,B=input().split()

if len(A)>len(B):
    print(A)
elif len(B)>len(A):
    print(B)
else:
    for i in range(len(A)):
        x=A[i]
        y=B[i]

        if x=="4" and y=="7":
            print(A)
            break
        if x=="7" and y=="4":
            print(B)
            break

        if x>y:
            print(A)
            break
        elif y>x:
            print(B)
            break