import sys
input=lambda: sys.stdin.readline().rstrip()
a,b=map(int,input().split())
aa,bb=str(a),str(b)
if len(aa)>len(bb):
  print(a)
elif len(aa)<len(bb):
  print(b)
else:
  for i in range(len(aa)):
    if int(aa[i])==4 and int(bb[i])==7:
      print(a)
      break
    elif int(aa[i])==7 and int(bb[i])==4:
      print(b)
      break
    elif int(aa[i])>int(bb[i]):
      print(a)
      break
    elif int(aa[i])<int(bb[i]):
      print(b)
      break
    else:
      continue