C++ :

#include<iostream>
using namespace std;
int main() {
	int a,b=1;
	cin >> a;
	for (int i = 1; i <= a; i++) {
		for (int j = 1; j <= a; j++) {
			cout << char(b + 64);
			b++;
		}
		cout << endl;
		b = b - a+1;
	}
}