[ICPC 2020 Shanghai R] Fibonacci

Luogu

IDLGP9825

Time1000ms

Memory1024MB

DifficultyP2

数学2020数论上海O2优化ICPC

In mathematics, the Fibonacci numbers, commonly denoted as $f_n$, is a sequence such that each number is the sum of the two preceding numbers, starting with $1$ and $1$. That is, $f_1 = 1, f_2 = 1$ and $f_n = f_{n-2} + f_{n-1}~(n \ge 3)$. Thus, the beginning of the sequence is $1, 1, 2, 3, 5, 8, 13, 21,\ldots$ . Given $n$, please calculate $\sum_{i=1}^{n}{\sum_{j=i+1}^{n}{g(f_i,f_j)}}$, where $g(x,y) = 1$ when $x \cdot y$ is even, otherwise $g(x,y) = 0$. ## Input The only line contains one integer $n~(1\le n\le 10^9)$. ## Output Output one number -- $\sum_{i=1}^{n}{\sum_{j=i+1}^{n}{g(f_i,f_j)}}$. [samples]

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API Response (JSON)

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    "name": "[ICPC 2020 Shanghai R] Fibonacci",
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      "content": "In mathematics, the Fibonacci numbers, commonly denoted as $f_n$, is a sequence such that each number is the sum of the two preceding numbers, starting with $1$ and $1$. That is, $f_1 = 1, f_2 = 1$ an",
      "description_type": "Markdown"
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    "platform": "Luogu",
    "limit": {
      "time_limit": 1000,
      "memory_limit": 1048576
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      "LuoguStyle": "P2"
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    "sign": "LGP9825"
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      "statement_type": "Markdown",
      "content": "In mathematics, the Fibonacci numbers, commonly denoted as $f_n$, is a sequence such that each number is the sum of the two preceding numbers, starting with $1$ and $1$. That is, $f_1 = 1, f_2 = 1$ an...",
      "is_translate": false,
      "language": "English"
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