A,B=input().split()
n=max(len(A),len(B))
aa=A.zfill(n)
bb=B.zfill(n)
for a,b in zip(aa,bb):
    if a==b:
        continue
    a=int(a);b=int(b)
    if (a==4 and b==7) or (a==7 and b==4):
        a,b=b,a
    if a>b:
        print(A)
        exit(0)
    else:
        print(B)
        exit(0)