#include <bits/stdc++.h>

using namespace std;

using ll = long long;

char solve(int n, const string& s) {
    int cnt = 0;
    for (int i = 0; i < n; ++i) {
        if (s[i] == 'x') continue;
        bool f = false;
        if (i + 2 < n) f |= (s[i + 1] == 'o' && s[i + 2] == 'o');
        if (i > 0 && i + 1 < n) f |= (s[i - 1] == 'o' && s[i + 1] == 'o');
        if (i > 1) f |= (s[i - 2] == 'o' && s[i - 1] == 'o');
        cnt += f;
    }
    return (cnt > 0 ? 'O' : 'X');
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int t;
    cin >> t;
    for (int i = 0; i < t; ++i) {
        int n;
        string s;
        cin >> n >> s;
        cout << solve(n, s) << "\n";
    }
    return 0;
}