{"trustable":false,"sections":[{"title":"","value":{"format":"MD","content":"Suppose we put two panes of glass back-to-back. Given $n$, how many way $C_n$ are there for light rays through or be reflected after changing direction $n$ times?\n\u003cbr\u003e\nFollowing figure shows the situation the value of $n$ is \u003ccode\u003e0\u003c/code\u003e, \u003ccode\u003e1\u003c/code\u003e and \u003ccode\u003e2\u003c/code\u003e.\n\u003cimg src\u003d\"https://i.ibb.co/XzCDP1c/lights.png\" alt\u003d\"example\" width\u003d\"600\"/\u003e\n\u003cbr\u003e\n\u003cb id\u003d\"input\"\u003eInput.\u003c/b\u003e It is a set of lines with an integer $n$ where $0 \\le n \\le 10^3$ in each of them.\n\u003cb id\u003d\"output\"\u003eOutput.\u003c/b\u003e For every one of these integers a line containing $C_n$ as described above. "}},{"title":"","value":{"format":"MD","content":"\u003cb id\u003d\"example1\"\u003eSample Input\u003c/b\u003e\n\u003ccode\u003e0\u003c/code\u003e\n\u003ccode\u003e1\u003c/code\u003e\n\u003ccode\u003e2\u003c/code\u003e\n\u003cbr\u003e\n\u003cb id\u003d\"example2\"\u003eSample Output\u003c/b\u003e\n\u003ccode\u003e1\u003c/code\u003e\n\u003ccode\u003e2\u003c/code\u003e\n\u003ccode\u003e3\u003c/code\u003e"}}]}