404A

#include<bits/stdc++.h>
#define lli long long int
#define vi vector<int>
#define vlli vector<lli>
#define pii pair<int,int>
#define vpi vector<pii>
#define mp unordered_map<char,int>
#define rep(i,a,b) for(int i=a;i<b;i++)
#define ff first
#define ss second
#define nline "\n"
#define pf cout
 
#define MOD1 1000000007
#define MOD2 1000000009
using namespace std;
int main()
{
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
 
  int n;cin>>n;
  string str;
  set<char>x,anything;
  for (int i=0;i<n;i++)
  {
    cin>>str;
    for(int j=0; j<n;j++){
      if (i==j || i+j==n-1){
        x.insert(str[j]);
      }
      else {
        anything.insert(str[j]);
      }
    }
  }
  /*for(auto it:x){
    pf<<it.begin()<<nline;}
 
  for (auto iti:anything){
       pf<<iti.begin()<<nline;
  }*/
  if (x.size()==1 && anything.size()==1 && *x.begin()!=*anything.begin()){ // significance of last condition is that ->
  //as it is a set , it'll store only 1 count of each type ...so it should be begin() and no such significance of end()
      pf<<"YES"<<nline;
    }
    else{
      pf<<"NO"<<nline;
    }
  return 0;
}