20 lines
305 B
Python
20 lines
305 B
Python
n = int(input())
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prev_t = 0
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prev_v = 0
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total = 0
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for i in range(n):
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m = input().split()
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t = int(m[0])
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v = float(m[1])
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if prev_t == 0:
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prev_t = t
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prev_v = v
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continue
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total += ((prev_v + v) / 2) * (t - prev_t) / 1000
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prev_t = t
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prev_v = v
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print(total)
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