#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
int main()
{
	char s1[1000];
	char s2[1000];
	scanf("%s", &s1);
	scanf("%s", &s2);
	int i = 0;
	int j = 0;
	int s1len = strlen(s1);
	int s2len = strlen(s2);
	if (s1len < s2len)
	{
		if (s1len == 1)
		{
			for (i = 0; i < s2len; i++)
			{
				if (s2[i] == s1[0])
				{
					printf("%c", s1[0]);
					printf(" is substring of ");
					for (i = 0; i < s2len; i++)
					{
						printf("%c", s2[i]);
					}
					return 0;
				}
			}
		}
		else
		{
			for (i = 0; i < s2len; i++)
			{
				if (s1[j] == s2[i])
				{
					j = j + 1;
				}
				else if (s1[j] != s2[i])
				{
					j = 0;
				}
				if (j == s1len)
				{
					for (j = 0; j < s1len; j++)
					{
						printf("%c", s1[j]);
					}
					printf(" is substring of ");
					for (i = 0; i < s2len; i++)
					{
						printf("%c", s2[i]);
					}
					return 0;
				}
			}
		}
	}
	else if (s2len < s1len)
	{
		if (s2len == 1)
		{
			for (j = 0; j < s1len; j++)
			{
				if (s1[j] == s2[0])
				{
					for (i = 0; i < s2len; i++)
					{
						printf("%c", s2[i]);
					}
					printf(" is substring of ");
					for (j = 0; j < s1len; j++)
					{
						printf("%c", s1[j]);
					}
					return 0;
				}
			}
		}
		else
		{
			for (j = 0; j < s1len; j++)
			{
				if (s1[j] == s2[i])
				{
					i = i + 1;
				}
				else if (s1[j] != s2[i])
				{
					i = 0;
				}
				if (i == s2len)
				{
					for (i = 0; i < s2len; i++)
					{
						printf("%c", s2[i]);
					}
					printf(" is substring of ");
					for (j = 0; j < s1len; j++)
					{
						printf("%c", s1[j]);
					}
					return 0;
				}
			}
		}
	}
	else if (s1len == s2len)
	{
		for (i = 0; i < s2len; i++)
		{
			if (s1[i] == s2[j])
			{
				j = j + 1;
			}
			else
			{
				break;
			}
		}
		if (i == s1len)
		{
			for (i = 0; i < s2len; i++)
			{
				printf("%c", s2[i]);
			}
			printf(" is substring of ");
			for (j = 0; j < s1len; j++)
			{
				printf("%c", s1[j]);
			}
			return 0;
		}
	}
	printf("No substring");
	return 0;
}