Vitaly is a diligent student who never missed a lesson in his five years of studying in the university. He always does his homework on time and passes his exams in time. 

During the last lesson the teacher has provided two strings *s* and *t* to Vitaly. The strings have the same length, they consist of lowercase English letters, string *s* is lexicographically smaller than string *t*. Vitaly wondered if there is such string that is lexicographically larger than string *s* and at the same is lexicographically smaller than string *t*. This string should also consist of lowercase English letters and have the length equal to the lengths of strings *s* and *t*. 

Let's help Vitaly solve this easy problem!
The first line contains string *s* (1 ≤ |*s*| ≤ 100), consisting of lowercase English letters. Here, |*s*| denotes the length of the string.

The second line contains string *t* (|*t*| = |*s*|), consisting of lowercase English letters.

It is guaranteed that the lengths of strings *s* and *t* are the same and string *s* is lexicographically less than string *t*.
s = input()
t = input()

index = 0 #index la vi tri khac nhau dau tien cua hai chuoi
for i in range(len(s)):
    if (s[i] != t[i]):
        index = i
        break
res = s[:index]
temp = ord(t[-1]) - ord(s[-1])
if (index != 0): #co nhieu hon mot ky tu
    if(index == len(s) - 1): #ky tu khac la vi tri cuoi cung
        #temp = ord(t[-1]) - ord(s[-1])
        if (temp == 1):
            print("No such string")
        else:
            res = res + chr(ord(s[-1]) + 1)
            print(res)
    else: #ky tu khac khong phai la ky tu cuoi cung
        res = res + s[index]
        for i in range(len(s) - index - 1):
            res = res + "a" #vi a la ky tu co lexicographically nho nhat
        print(res)
else: #khong khac ky tu nao hoac hai chuoi da cho co do dai la 1
    if(len(s) != 1):
        print("No such string")
    else:
        if(temp == 1):
            print("No such string")
        else:
            print(chr(ord(s[-1]) + 1))


