A,B=list(map(int,input().split()))

Aa=[int(x) for x in list(str(A))]
Bb=[int(x) for x in list(str(B))]

la=len(Aa)
lb=len(Bb)

if(la>lb):
    print(A)
    
elif(lb>la):
    print(B)
    
else:
    for i in range(la):
        if(Aa[i]==4 and Bb[i]==7):
            print(A)
            break
        elif(Aa[i]==7 and Bb[i]==4):
            print(B)
            break
        else:
            if(Aa[i]>Bb[i]):
                print(A)
                break
            elif(Aa[i]<Bb[i]):
                print(B)
                break