+ محدودیت زمان: ۱ ثانیه + محدودیت حافظه: ۲۵۶ مگابایت ---------- Arts and literature have always been influenced by science. This appears, for example, in Christopher Nolan movies. But, there is a scientist who is doing his research on a hypothesis based on fictional novels. Dr. Khosro, a theoretical physicist, does research on parallel worlds with high-dimensions, inspired by Isaac Asimov’s novels. During his research, he needs a method of sorting in his imaginary high-dimension network of planets. In Dr. Khosro’s imaginary n-dimensional world, there are $2^n$ planets and a wormhole network connecting them. The network is like an $n$-dimensional hypercube. The planets are numbered with non-negative integers less than $2^n$, and there is a wormhole from planet a to planet b if and only if the n-bit binary representations of $a$ and $b$ differ in exactly one bit-position. In Dr. Khosro’s model, there is a number written on each planet and we can swap the numbers of two planets only if there is a direct wormhole between them. You are given the numbers written on each planet, construct a valid sequence of swaps that makes the numbers sequence sorted from smallest to largest. Formally, if the number written on the planet number $i$ ($0 \leq i \lt 2^n$) is denoted by $a_i$, you have to construct a sequence of valid pairwise swaps that makes the sequence $a = \langle a_0, a_1, \dots, a_{2^{n-1}} \rangle$ in increasing order. # ورودی The first line of input consists of $n$ ($1 \leq n \leq 10$), the dimension of Dr. Khosro’s imaginary world. The next line contains $2^n$ **distinct** integers, indicating $a_0, a_1, \dots, a_{2^{n-1}} \; (0 \leq a_i \leq 10^6)$. # خروجی Print the numbers of your swaps in the first line. Your answer will be considered correct if this number is nonnegative and less than $12,000$. Then in the following lines, print the sequence of swaps. In your solution, every swap must be between two planets with a direct wormhole between them. # مثال‌‌ها ## ورودی نمونه ۱ ``` 2 3 2 10 4 ```` ## خروجی نمونه ۱ ``` 2 1 0 3 2 ```` ## ورودی نمونه ۲ ``` 1 10 100 ```` ## خروجی نمونه ۲ ``` 0 ````