python
N = int(input()) data = list(map(int, input().split())) step = 0 seat = {x:i for (i,x) in enumerate(data)} def find_partner(x): if x%2 == 0: return x+1 else: return x-1 for i in range(0, 2*N, 2): x = data[i] j = seat[find_partner(x)] if abs(i-j) > 1: data[i+1], data[j] = data[j], data[i+1] seat[data[i+1]], seat[data[j]] = i+1, j step += 1 print(str(step))