{"trustable":true,"sections":[{"title":"","value":{"format":"HTML","content":"\u003cdiv class\u003d\"problem_par\"\u003e\u003cdiv class\u003d\"problem_par_normal\"\u003eThere is a certain amount of night guards that are available to protect the local junkyard from possible junk robberies. These guards need to be scheduled in pairs so that each pair guards in a different night. The junkyard CEO ordered you to write a program which given the guards characteristics determines the maximum amount of scheduled guards (the rest will be fired). Please note that each guard can be scheduled with only one of his colleagues and no guard can work alone.\r\n\u003c/div\u003e\u003c/div\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cdiv class\u003d\"problem_par\"\u003e\u003cdiv class\u003d\"problem_par_normal\"\u003eThe first line of the input contains one number \u003ci\u003eN\u003c/i\u003e ≤ 222 which is a number of night guards. Unlimited number of lines consisting of unordered pairs (\u003ci\u003ei\u003c/i\u003e,\u0026nbsp;\u003ci\u003ej\u003c/i\u003e) follow, each such pair means that guard #\u003ci\u003ei\u003c/i\u003e and guard #\u003ci\u003ej\u003c/i\u003e can work together, because it is possible to find uniforms that suit both of them (The junkyard uses different parts of uniforms for different guards i.e. helmets, pants, jackets. It is impossible to put small helmet on a guard with a big head or big shoes on guard with small feet). The input ends with Eof.\u003c/div\u003e\u003c/div\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cdiv class\u003d\"problem_par\"\u003e\u003cdiv class\u003d\"problem_par_normal\"\u003eYou should output one possible optimal assignment. On the first line of the output write the even number \u003ci\u003eC\u003c/i\u003e, the amount of scheduled guards. Then output \u003ci\u003eC\u003c/i\u003e/2 lines, each containing 2 integers (\u003ci\u003ei\u003c/i\u003e,\u0026nbsp;\u003ci\u003ej\u003c/i\u003e) that denote that \u003ci\u003ei\u003c/i\u003e and \u003ci\u003ej\u003c/i\u003e will work together.\u003c/div\u003e\u003c/div\u003e"}},{"title":"Sample","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e3\r\n1 2\r\n2 3\r\n1 3\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e2\r\n1 2\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}}]}