Lucas Number

AtCoder

IDabc079_b

Time2000ms

Memory256MB

Difficulty—

It is November $18$ now in Japan. By the way, $11$ and $18$ are adjacent Lucas numbers. You are given an integer $N$. Find the $N$\-th Lucas number. Here, the $i$\-th Lucas number $L_i$ is defined as follows: * $L_0=2$ * $L_1=1$ * $L_i=L_{i-1}+L_{i-2} (i≥2)$ ## Constraints * $1≤N≤86$ * It is guaranteed that the answer is less than $10^{18}$. * $N$ is an integer. ## Input Input is given from Standard Input in the following format: $N$ [samples]

Samples

Input #1

Output #1

11

*   $L_0=2$
*   $L_1=1$
*   $L_2=L_0+L_1=3$
*   $L_3=L_1+L_2=4$
*   $L_4=L_2+L_3=7$
*   $L_5=L_3+L_4=11$

Thus, the $5$\-th Lucas number is $11$.

Input #2

Output #2

939587134549734843

API Response (JSON)

{
  "problem": {
    "name": "Lucas Number",
    "description": {
      "content": "It is November $18$ now in Japan. By the way, $11$ and $18$ are adjacent Lucas numbers. You are given an integer $N$. Find the $N$\\-th Lucas number. Here, the $i$\\-th Lucas number $L_i$ is defined as ",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "abc079_b"
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  "statements": [
    {
      "statement_type": "Markdown",
      "content": "It is November $18$ now in Japan. By the way, $11$ and $18$ are adjacent Lucas numbers.\nYou are given an integer $N$. Find the $N$\\-th Lucas number.\nHere, the $i$\\-th Lucas number $L_i$ is defined as ...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

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