#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define MT make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
#define RT return
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;

void solve() {
    int T;
    cin >> T;
    while (T--) {
        int N;
        string S;
        cin >> N >> S;
        char ans = 'X';
        auto f = [&](int i) {
            if (i + 3 > N)return false;
            int x = 0, o = 0;
            FOR(j, i, i + 3) {
                if (S[j] == 'x')x++;
                else if (S[j] == 'o')o++;
            }
            return x == 0 && o >= 2;
        };

        rep(i, N) if (f(i)) ans = 'O';
        
        // ダブルリーチを作れる
        FOR(i, 2, N - 2) if (S[i] == '-') {
            if (((S[i - 2] == 'o'&&S[i - 1] == '-') || (S[i - 2] == '-'&&S[i - 1] == 'o'))
                && ((S[i + 1] == 'o' && S[i + 2] == '-') || (S[i + 1] == '-' && S[i + 2] == 'o'))) {
                ans = 'O';
            }
        }

        cout << ans << endl;
    }
}

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout << fixed << setprecision(15);
	solve();
	return 0;
}