P3103 [USACO14FEB] Airplane Boarding G

FJ's cows have decided to take a vacation, and have miraculously managed to find an airline willing to sell them tickets. When they arrive at the airport and start boarding their plane, they face an interesting problem, however. The airplane has N seats, which we model as the points x=1 through x=N on the number line. All N cows (1

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Initially, the cows are situated like this: cows -> 123 123