There are $20$ geese numbered $1-20$ standing in a line. The even-numbered geese are standing at the front in the order $2,4,\dots,20,$ where $2$ is at the front of the line. Then the odd-numbered geese are standing behind them in the order $1,3,5,\dots,19,$ where $19$ is at the end of the line. The geese want to rearrange themselves in order, so that they are ordered $1,2,\dots,20$ (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?

Let's think step by step and output the final answer within \boxed{}.
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