Islands War

AtCoder

IDabc103_d

Time2000ms

Memory256MB

Difficulty—

There are $N$ islands lining up from west to east, connected by $N-1$ bridges. The $i$\-th bridge connects the $i$\-th island from the west and the $(i+1)$\-th island from the west. One day, disputes took place between some islands, and there were $M$ requests from the inhabitants of the islands: Request $i$: A dispute took place between the $a_i$\-th island from the west and the $b_i$\-th island from the west. Please make traveling between these islands with bridges impossible. You decided to remove some bridges to meet all these $M$ requests. Find the minimum number of bridges that must be removed. ## Constraints * All values in input are integers. * $2 \leq N \leq 10^5$ * $1 \leq M \leq 10^5$ * $1 \leq a_i < b_i \leq N$ * All pairs $(a_i, b_i)$ are distinct. ## Input Input is given from Standard Input in the following format: $N$ $M$ $a_1$ $b_1$ $a_2$ $b_2$ $:$ $a_M$ $b_M$ [samples]

Samples

Input #1

5 2
1 4
2 5

Output #1

1

The requests can be met by removing the bridge connecting the second and third islands from the west.

Input #2

Output #2

Input #3

Output #3

API Response (JSON)

{
  "problem": {
    "name": "Islands War",
    "description": {
      "content": "There are $N$ islands lining up from west to east, connected by $N-1$ bridges. The $i$\\-th bridge connects the $i$\\-th island from the west and the $(i+1)$\\-th island from the west. One day, disputes ",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "abc103_d"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "There are $N$ islands lining up from west to east, connected by $N-1$ bridges.\nThe $i$\\-th bridge connects the $i$\\-th island from the west and the $(i+1)$\\-th island from the west.\nOne day, disputes ...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

Full JSON Raw Segments