Score : $100$ points

问题描述

AtCoder Inc. 通过其线上商店销售商品。

高桥决定从那里购买 $N$ 种不同类型的商品。
对于从 $1$ 到 $N$ 的每个整数 $i$，第 $i$ 类商品的单价为 $P_i$ 日元，他将购买 $Q_i$ 件该商品。

另外，他还必须支付运费。
如果购买商品的总价达到或超过 $S$ 日元，则运费为 $0$ 日元，否则运费为 $K$ 日元。

他需要支付购买商品的总价加上运费。
请计算他总共需要支付的金额。

以上为通义千问 qwen-max 翻译，仅供参考。

Problem Statement

AtCoder Inc. sells merchandise through its online shop.

Takahashi has decided to purchase $N$ types of products from there.
For each integer $i$ from $1$ to $N$, the $i$-th type of product has a price of $P_i$ yen each, and he will buy $Q_i$ of this.

Additionally, he must pay a shipping fee.
The shipping fee is $0$ yen if the total price of the products purchased is $S$ yen or above, and $K$ yen otherwise.

He will pay the total price of the products purchased plus the shipping fee.
Calculate the amount he will pay.

Constraints

• $1\leq N\leq 100$
• $1\leq S\leq 10000$
• $1\leq K\leq 10000$
• $1\leq P_i\leq 10000$
• $1\leq Q_i\leq 100$
• All input values are integers.

Input

The input is given from Standard Input in the following format:

$N$ $S$ $K$

$P_1$ $Q_1$

$P_2$ $Q_2$

$\vdots$

$P_N$ $Q_N$

Output

Print the amount Takahashi will pay for online shopping.

Sample Input 1

2 2000 500
1000 1
100 6

Sample Output 1

2100

Takahashi buys one product for $1000$ yen and six products for $100$ yen each.
Thus, the total price of the products is $1000\times 1+100\times 6=1600$ yen.
Since the total amount for the products is less than $2000$ yen, the shipping fee will be $500$ yen.
Therefore, the amount Takahashi will pay is $1600+500=2100$ yen.

Sample Input 2

3 2000 500
1000 1
100 6
5000 1

Sample Output 2

6600

The total price of the products is $1000\times 1+100\times 6+5000\times 1=6600$ yen.
Since the total amount for the products is not less than $2000$ yen, the shipping fee will be $0$ yen.
Therefore, the amount Takahashi will pay is $6600+0=6600$ yen.

Sample Input 3

2 2000 500
1000 1
1000 1

Sample Output 3

2000

There may be multiple products with the same price per item.

update @ 2024/3/10 01:16:46