6 lines
285 B
Python
6 lines
285 B
Python
N = int(input())
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points = [list(map(int, input().split())) for i in range(N)]
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points += [points[0]]
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N +=1
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print("%.1f" % (abs(sum(points[i][0] * points[j][1] for i, j in zip(range(N - 1), range(1, N))) - sum(points[j][0] * points[i][1] for i, j in zip(range(N - 1), range(1, N))))/2))
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