#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <set>
#include <map>

using namespace std;
typedef long long ll;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int T;
    cin >> T;
    for(int d = 0; d < T; d++){
        int N;
        string S;
        cin >> N >> S;
        bool ok = false;
        for(int i = 0; i+2 < N; i++){
            if(S[i] == 'o' && S[i+1] == 'o' && S[i+2] == '-') ok = true;
            if(S[i] == '-' && S[i+1] == 'o' && S[i+2] == 'o') ok = true;
            if(S[i] == 'o' && S[i+1] == '-' && S[i+2] == 'o') ok = true;
            if(S[i] == 'o' && S[i+1] == 'o' && S[i+2] == 'o') ok = true;
        }
        for(int i = 0; i+3 < N; i++){
            if(S[i] == '-' && S[i+1] == 'o' && S[i+2] == '-' && S[i+3] == '-') ok = true;
            if(S[i] == '-' && S[i+1] == '-' && S[i+2] == 'o' && S[i+3] == '-') ok = true;
        }
        int cnto = 0;
        int cntx = 0;
        int cnt_ = 0;
        for(int i = 0; i < N; i++){
            if(S[i] == 'x') {
                cntx++;
            }
            if(S[i] == '-') cnt_++;
            if(S[i] == 'o'){
                if((cnto > 0) && (cnt_%2 == 1) && (cntx == 0)) {
                    if(ok == false) return -1;
                    ok = true;
                }
                // if(cnt_%2 == 1 ) ok = true;
                cnt_ = 0;
                cntx = 0;
                cnto++;
            }
        }
        if(ok) cout << 'O' << endl;
        else cout << 'X' << endl;
    }
}