Pay attention: this problem is interactive. Penguin Xoriy came up with a new game recently. He has n icicles numbered from 1 to n . Each icicle has a temperature — an integer from 1 to 10 9 . Exactly two of these icicles are special: their temperature is y , while a temperature of all the others is x ≠ y . You have to find those special icicles. You can choose a non-empty subset of icicles and ask the penguin what is the bitwise exclusive OR ( XOR ) of the temperatures of the icicles in this subset. Note that you can't ask more than 19 questions. You are to find the special icicles. The first line contains three integers n , x , y ( 2 ≤ n ≤ 1000 , 1 ≤ x , y ≤ 10 9 , x ≠ y ) — the number of icicles, the temperature of non-special icicles and the temperature of the special icicles. To give your answer to the penguin you have to print character "!" (without quotes), then print two integers p 1 , p 2 ( p 1 < p 2 ) — the indexes of the special icicles in ascending order . Note that "!" and p 1 should be separated by a space; the indexes should be separated by a space too. After you gave the answer your program should terminate immediately. To ask a question print character "?" (without quotes), an integer c ( 1 ≤ c ≤ n ), and c distinct integers p 1 , p 2 , ..., p c ( 1 ≤ p i ≤ n ) — the indexes of icicles that you want to know about. Note that "?" and c should be separated by a space; the indexes should be separated by a space too. After you asked the question, read a single integer — the answer. Note that you can't ask more than 19 questions. If you ask more than 19 questions or at least one incorrect question, your solution will get " Wrong answer ". If at some moment your program reads - 1 as an answer, it should immediately exit (for example, by calling exit(0)). You will get " Wrong answer " in this case, it means that you asked more than 19 questions, or asked an invalid question. If you ignore this, you can get other verdicts since your program will con