// yukicoder: No.517 壊れたアクセサリー
// 2019.6.26 bal4u

#include <stdio.h>

#if 1
#define gc() getchar_unlocked()
#define pc(c) putchar_unlocked(c)
#else
#define gc() getchar()
#define pc(c) putchar(c)
#endif
int in() {
	int n = 0, c = gc();
	do n = 10 * n + (c & 0xf), c = gc(); while (c >= '0');
	return n;
}

int ins(char *s) {
	char *p = s;
	do *s = gc();
	while (*s++ > ' ');
	*--s = 0;
	return s - p;
}

void outs(char *s) { while (*s) pc(*s++); }

typedef struct { int p, n; } T;
T t[30];
int nex[30];
char a[30], f[30];

int main()
{
	int i, j, k, N, w, top;

	for (j = 0; j < 2; j++) {
		N = in();
		for (i = 0; i < N; i++) {
			w = ins(a);
			for (k = 0; k < w; k++) {
				int c = a[k] - 'A' + 1;
				f[c] = 1;
				if (k > 0) t[c].p = a[k-1]-'A'+1;
				if (k < w-1) t[c].n = a[k+1]-'A'+1;
			}
		}
	}
	top = 0;
	for (i = 1; i <= 27; i++) if (f[i]) {
		if (t[i].p == 0) {
			if (top) { outs("-1\n"); return 0; }
			top = i;
		}
	}
	while (top) {
		pc(top+'A'-1);
		top = t[top].n;
	}
	pc('\n');
}