#include <iostream>
using namespace std;
int main(){
  int t;cin>>t;
  while(t--){
    int n;string s;cin>>n>>s;
    int z = 0;
    for(int i = 0; n > i; i++){
      if(s[i]=='o'){
        if(n!=i+1 && s[i+1]=='o'){
          if((i&&s[i-1]!='x')||(n!=i+2&&s[i+2]!='x')){
            //cout << i << 1 << endl;
            cout << "O" << endl;
            z++;
            break;
          }
        }else if(n!=i+2 && s[i+2]=='o' && s[i+1]=='-'){
          //cout << i << 2 << endl;
          cout << "O" << endl;
          z++;
          break;
        }else{
          if(i>1 && i+2 <= n){
            bool l = true;
            for(int j = i-2; i+2 >= j; j++){
              if(s[j]=='x'){
                l=false;
                break;
              }
            }
          
            if(l){
              cout << "O" << endl;
              z++;
            }
          }
        }
      }
    }
    if(!z){
      cout << "X" << endl;
    }
  }
}