//CodeForces 404A
1 #include "iostream"
2 #include "cstdio"
3 #include "cstring"
4 #include "algorithm"
5 using namespace std;
6 char mat[310][310];
7 int n;
8 bool check_1()
9 {
10 int i;
11 char c = mat[1][1];
12 for(i = 1; i <= n; ++i) {
13 if(c != mat[i][i] || c != mat[i][n + 1 - i])
14 return 0;
15 }
16 return 1;
17 }
18
19 bool check_2()
20 {
21 int i, j;
22 char c = mat[1][2];
23 for(i = 1; i <= n; ++i) {
24 for(j = 1; j <= n; ++j) {
25 if(i == j || n + 1 - i == j)
26 continue;
27 if(c != mat[i][j])
28 return 0;
29 }
30 }
31 return 1;
32 }
33
34 int main()
35 {
36 int i, j;
37 scanf("%d", &n);
38 for(i = 1; i <= n; ++i)
39 scanf("%s", mat[i] + 1);
40 if(mat[1][1] != mat[1][2] && check_1() && check_2())
41 printf("YES
");
42 else
43 printf("NO
");
44 }