n = int(input())
a = [input() for _ in range(n)]
if n == 1:
    print('a' if a[0] == 'b' else 'b')
    exit()
b = []
for i in range(n):
    o = 0
    for j in range(n):
        if a[i][j] == 'a':
            o += 1
    b.append(o)
b.sort()
for i in range(n-1):
    if b[i]+1 != b[i+1]:
        print('a'*(b[i]+1) + 'b'*(n-b[i]-1))
        exit()
print('a'*n)