1
n = int(input())
2
table = [input() for i in range(n)]
3
 
4
if table[0][0] == table[1][0]:
5
    print('NO')
6
    exit(0)
7
 
8
for i in range(n):
9
    if table[0][0] != table[i][i]:
10
        print('NO')
11
        exit(0)
12
    if table[0][0] != table[i][n - 1 - i]:
13
        print('NO')
14
        exit(0)
15
    
16
for i in range(n):
17
    for j in range(n):
18
        if i != j and i + j != n - 1: 
19
            if table[1][0] != table[i][j]:
20
                print('NO')
21
                exit(0)
22
print('YES')