#include "bits/stdc++.h"
using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
#define int long long

string solve(string t) {
	if (t.size() < 3)return "X";
	rep(i, t.size() - 2) {
		string h;
		h.push_back(t[i]); h.push_back(t[i + 1]); h.push_back(t[i + 2]);
		if (h == "-oo" || h == "oo-" || h == "ooo" || h == "o-o")return "O";
		if (i != t.size() - 3) {
			h.push_back(t[i + 3]);
			if (h == "--o-" || h == "-o--")return "O";
		}
	}
	return "X";
}

signed main() {
	int t; cin >> t;
	while (t) {
		t--;
	
		int n; cin >> n; string s; cin >> s;
		cout << solve(s) << endl;
	}
}