I have geeeesse

There are 20 geese numbered 1 through 20 standing in a line. The even numbered geese are standing at the front in the order 2, 4, . . . , 20, where 2 is at the front of the line. Then the odd numbered geese are standing behind them in the order, 1, 3, 5, . . . , 19, where 19 is at the end of the line. The geese want to rearrange themselves in order, so that they are ordered 1, 2, . . . , 20 (1 is at the front), and they do this by successively swapping two adjacent geese. What is the minimum number of swaps required to achieve this formation?