#include<stdio.h>
#include<string.h>
void search(char[], char[]);
int main() {
	char s[100],t[100];
        gets(s);
        gets(t);
	search(s,t);
	return (0);
}
/*
void search(char src[], char str[]) {
	int i=0, j=0, flag,u=0,v=0;
	u=strlen(src);
	v=strlen(str);
	while (src[i] != '\0') {
		for(i=0;i<u;i++){
			for(j=0;j<v;j++){
				if(src[i]==str[j]&& str[j]!='\0')
					flag=1;
				else
					flag=0;
					break;
			}
		}
	}
	if(flag==1)
		printf("%s", str[j]);
	else
		printf("NULL");
}
*/
void search(char src[], char str[]) {
	int i=0, j=0, flag=0,f;
	while (src[i] != '\0') {
		while (src[i] != str[0] && src[i] != '\0')
			i++;
		if (src[i] == '\0')
			return (-1);
		f = i;
		while (src[i] == str[j] && src[i] != '\0' && str[j] != '\0') {
			i++;
			j++;
		}
		if (str[j] == '\0')
			flag=1;
		if (src[i] == '\0')
			flag=0;
		i = f + 1;
		j = 0;
	}
	if(flag==1)
		printf("%s", str[j]);
	else
		printf("NULL");
}