A, B = input().split()

if len(A) == len(B):
    
    for i in range(len(A)):
        
        if A[i] != B[i]:
            
            if (A[i] == '4' and B[i] == '7'):
                
                print(A)
                
            elif (A[i] == '7' and B[i] == '4'):
                
                print(B)
                
            elif int(A[i]) > int(B[i]):
                
                print(A)
                
            else:
                
                print(B)
                
            exit()
            
else:
    
    if len(A) > len(B):
        
        print(A)
        
    else:
        
        print(B)