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))]

d={}
for i in range(0,10):
    d[i]=i
d[4]=7
d[7]=4

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

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