#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> P;
typedef long long ll;
typedef long double ld;
const int inf=1e9+7;
const ll longinf=1LL<<60;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
#define F first
#define S second

const int mx=8010;
const ll mod=1e9+7;
 
int main(){
  int t;
  cin >> t;
while(t--){
  int n;
  string s;
  cin >> n >> s;
  if(n<6){ cout<<"X"<<endl; continue; }
  cout<<(regex_search(s,regex("(ooo|oo-|-oo|o-o|--o-|-o--)"))?"O":"X")<<endl;
}
  return 0;
}