There exists a coin minting machine at Bi0S which is known for its extermely fast minting process. However out of every batch (N coins) it produces one coin is faulty (have a different weight compared to the other N-1 coins). You can get information of the xor of the weight of the coins from index i to index j (both included) by communicating with the minting machine. Find the faulty coin (coin with different weight) with minimum number of queries, as the minting machine has better things to do than answer your questions. Multiple batches are produced by the minting machine and it is gaurenteed that in each batch there is only one defective coin. Your query should be in the format "i j" (without the quotes) where both i and j should lie in the range [0, N). You can report the correct position (Of course after solving it) in the format "! index" (without the quotes) where index lies in the range [0, N). If you correctly identify the faulty coin for a batch, you will continue to the next batch. If a query is given in the wrong format or give a wrong answer you will be rejected.