Energy Drink Collector

AtCoder

IDabc121_c

Time2000ms

Memory256MB

Difficulty—

Hearing that energy drinks increase rating in those sites, Takahashi decides to buy up $M$ cans of energy drinks. There are $N$ stores that sell energy drinks. In the $i$\-th store, he can buy at most $B_i$ cans of energy drinks for $A_i$ yen (the currency of Japan) each. What is the minimum amount of money with which he can buy $M$ cans of energy drinks? It is guaranteed that, in the given inputs, a sufficient amount of money can always buy $M$ cans of energy drinks. ## Constraints * All values in input are integers. * $1 \leq N, M \leq 10^5$ * $1 \leq A_i \leq 10^9$ * $1 \leq B_i \leq 10^5$ * $B_1 + ... + B_N \geq M$ ## Input Input is given from Standard Input in the following format: $N$ $M$ $A_1$ $B_1$ $A_2$ $B_2$ $\vdots$ $A_N$ $B_N$ [samples]

Samples

Input #1

2 5
4 9
2 4

Output #1

12

With $12$ yen, we can buy one drink at the first store and four drinks at the second store, for the total of five drinks. However, we cannot buy $5$ drinks with $11$ yen or less.

Input #2

Output #2

Input #3

1 100000
1000000000 100000

Output #3

100000000000000

The output may not fit into a $32$\-bit integer type.

API Response (JSON)

{
  "problem": {
    "name": "Energy Drink Collector",
    "description": {
      "content": "Hearing that energy drinks increase rating in those sites, Takahashi decides to buy up $M$ cans of energy drinks. There are $N$ stores that sell energy drinks. In the $i$\\-th store, he can buy at most",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "abc121_c"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "Hearing that energy drinks increase rating in those sites, Takahashi decides to buy up $M$ cans of energy drinks.\nThere are $N$ stores that sell energy drinks. In the $i$\\-th store, he can buy at most...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

Full JSON Raw Segments