#include <iostream>
#include <string>
using namespace std;

int N;

struct pt{
	int x,y;
};

int distSq(pt p1, pt p2){
	return (p2.x-p1.x)*(p2.x-p1.x) + (p2.y-p1.y)*(p2.y-p1.y) - (p2.x-p1.x)*(p2.y-p1.y);
}

int main() {
	while(cin >> N){
		if(N == 0) return 0;
		string s;
		cin >> s;
		pt points[26][3];
		int pointNum[26] = {0};
		int offset = 0;
		for(int i = 0; i < N; i++){
			for(int j = 0; j <= i; j++){
				char c = s[offset];
				points[c-'a'][pointNum[c-'a']].x = i, points[c-'a'][pointNum[c-'a']].y = j;
				offset++;
				pointNum[c-'a']++;
			}
		}
		int cnt = 0;
		for(int i = 0; i < 26; i++){
			if(pointNum[i] != 3) continue;
			int d1 = distSq(points[i][0], points[i][1]);
			int d2 = distSq(points[i][0], points[i][2]);
			int d3 = distSq(points[i][1], points[i][2]);
			if(d1 == d2 && d2 == d3){
				cnt++;
				cout << (char)(i+'a');
			}
		}
		if(cnt == 0) cout << "LOOOOOOOOSER!";
		cout << endl;
	}
	return 0;
}