T=int(input())
for i in range(T):
  N,S=input().split()
  N=int(N)
  flag=True
  for i in range(N-2):
    if S[i]==S[i+1]==S[i+2]=="o":
      print("O")
      flag=False
      break
    if (S[i]==S[i+1]=="o") and S[i+2]=="-":
      print("O")
      flag=False
      break
    if (S[i]==S[i+2]=="o") and S[i+1]=="-":
      print("O")
      flag=False
      break
    if (S[i+2]==S[i+1]=="o") and S[i]=="-":
      print("O")
      flag=False
      break
    if i!=N-3:
      if (S[i+1]=="o") and S[i]==S[i+2]==S[i+3]=="-":
        print("O")
        flag=False
        break
      if (S[i+2]=="o") and S[i]==S[i+1]==S[i+3]=="-":
        print("O")
        flag=False
        break
  if flag:
    print("X")