{"trustable":true,"sections":[{"title":"","value":{"format":"HTML","content":"\u003cstyle type\u003d\"text/css\"\u003e .sampledata { font-family: \"Courier New\", Courier, monospace; white-space: pre; }\u003c/style\u003e\u003cdiv\u003e\n 有三个好朋友喜欢在一起玩游戏,A君写下一个字符串S,B君将其复制一遍得到T,C君在T的任意位置(包括首尾)插入一个字符得到U.现在你得到了U,请你找出S.\n\u003c/div\u003e \n\u003cp\u003e\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cdiv\u003e \n \u003cdiv\u003e\n 第一行一个数N,表示U的长度.\n \u003c/div\u003e \n \u003cdiv\u003e\n 第二行一个字符串U,保证U由大写字母组成\n \u003c/div\u003e \n\u003c/div\u003e \n\u003cp\u003e\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cdiv\u003e \n \u003cdiv\u003e\n 输出一行,若S不存在,输出\"NOT POSSIBLE\".若S不唯一,输出\"NOT UNIQUE\".否则输出S.\n \u003c/div\u003e \n\u003c/div\u003e \n\u003cp\u003e\u003c/p\u003e"}},{"title":"Sample Input","value":{"format":"HTML","content":"\u003cspan class\u003dsampledata\u003eSample Input1:\r\n7\r\nABXCABC\r\n\r\n\r\nSample Input2:\r\n\r\n6\r\nABCDEF\r\n\r\nSample Input3:\r\n\r\n9\r\nABABABABA\u003c/span\u003e\u003c/div\u003e"}},{"title":"Sample Output","value":{"format":"HTML","content":"\u003cspan class\u003dsampledata\u003eSample Output1:\r\n\r\nABC\r\n\r\nSample Output2:\r\n\r\nNOT POSSIBLE\r\n\r\nSample Output3:\r\n\r\nNOT UNIQUE\u003c/span\u003e\u003c/div\u003e"}},{"title":"Hint","value":{"format":"HTML","content":"\u003cp\u003e\u003c/p\u003e\n\u003cdiv\u003e\n 对于100%的数据 2\u0026lt;\u003dN\u0026lt;\u003d2000001\n\u003c/div\u003e\n\u003cbr\u003e \n\u003cdiv\u003e\u003c/div\u003e\n\u003cbr\u003e \n\u003cp\u003e\u003c/p\u003e\n\u003cp\u003e\u003c/p\u003e"}}]}