P3430 [POI 2005] DWU-Double-row

$2n$ soldiers are standing in a double-row. They have to be rearranged, so that there are no equally tall soldiers in each row - then we shall say, that the soldiers are set up properly. A single operation consists in swapping two soldiers who occupy the same position (but in different rows). Your task is to determine the minimum number of swaps necessary to set the soldiers up properly. Example: There is a double-row of $18$ soldiers in the figure. Arrows indicate the swaps that rearrange the soldiers in a proper way. TaskWrite a programme that: reads from the standard input the number and heights of soldiers, as they stand initially,determines the minimum number of swaps (of soldiers standing on the same position in different rows) necessary to set up soldiers properly,writes the result to the standard output. **一句话题意By Scarlet：$2n$个数站成两排（每个数在$2n$个数中最多出现两遍），一次操作可以交换任意一列中两个数，求使每行数不重复的最少操作数。**

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