s1 = input()
s2 = input()
end1=len(s1)-1
end2=len(s2)-1
set_s1 = set(s1)
set_s2 = set(s2)

if set_s1 & set_s2:

    if end1<end2:
        for i in s2:
            if s1[0]==i:
                part=s2[s2.index(i):s2.index(i)+len(s1)]
                if part == s1:
                    print('{} is substring of {}'.format(s1,s2))
                    break
                else :
                    print("No substring")
                    break



    if end1>end2:
        for i in s1:
            if s2[0]==i:
                part=s1[s1.index(i):s1.index(i)+len(s2)]
                if part == s2:
                    print('{} is substring of {}'.format(s2,s1))
                    break
                else :
                    print("No substring")
                    break
else:
    print("No substring")