#include<bits/stdc++.h>
using namespace std;
int n,ss,vis[305];
char mapp[305][305];
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			cin>>mapp[i][j];
			if(!vis[mapp[i][j]]){
				vis[mapp[i][j]]=1;
				ss++;
			}
		}
	}
	if(ss!=2||mapp[1][1]==mapp[1][2]){
		cout<<"NO";
		return 0;
	}
	for(int i=1;i<=n;i++){
		if(mapp[i][i]!=mapp[1][1]||mapp[i][n-i+1]!=mapp[1][1]){
			cout<<"NO";
			return 0;
		}
		mapp[i][i]=mapp[i][n-i+1]=mapp[1][2];
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			if(mapp[i][j]!=mapp[1][2]){
				cout<<"NO";
				return 0;
			}
		}
	}
	cout<<"YES";
	return 0;
}