#include "stdio.h"
#include "string.h"

#define MAX_LEN 1000


int main()
{
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);

    char s1[MAX_LEN];
    char s2[MAX_LEN];
    char buf[MAX_LEN];
    int buf_p = 0;

    scanf("%s", s1);
    scanf("%s", s2);

    for (int i = 0; i < strlen(s2); ++i) {
        int count = 0;
        for (int j = 0; j < strlen(s2); ++j) {
            if (s2[i] == s2[j]) {
                ++count;
            }
            if (count > 2) {
                printf("NO");
                return 0;
            }
        }
        int good = 0;
        if (count == 2) good = 1;
        for (int j = 0; j < strlen(s2); ++j) {
            if (s1[j] == s2[i]) {
                good = 1;
                buf[buf_p] = s1[j];
                ++buf_p;
                break;
            }
        }
        if (good != 1) {
            printf("NO");
            return 0;
        }
    }

    printf("%s%s", s2, buf);
    return 0;
}