103320: [Atcoder]ABC332 A - Online Shopping

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.

问题描述

AtCoder Inc.通过其在线商店销售商品。

Takahashi决定在那里购买$N$种产品。
对于从1到$N$的每个整数$i$，第$i$种产品每件价格为$P_i$日元，他将购买$Q_i$件这个产品。

此外，他还必须支付运费。
如果购买的产品的总价格为$S$日元或以上，运费为0日元，否则为$K$日元。

他将支付购买的产品的总价格加上运费。
计算他将支付的金额。

约束

• $1\leq N\leq 100$
• $1\leq S\leq 10000$
• $1\leq K\leq 10000$
• $1\leq P_i\leq 10000$
• $1\leq Q_i\leq 100$
• 所有输入值都是整数。

输入

输入从标准输入以以下格式给出:

$N$ $S$ $K$
$P_1$ $Q_1$
$P_2$ $Q_2$
$\vdots$
$P_N$ $Q_N$

输出

打印Takahashi在线购物将支付的金额。

样例输入1

2 2000 500
1000 1
100 6

样例输出1

2100

Takahashi以1000日元的价格购买了一件产品，并以100日元的价格购买了6件产品。
因此，产品的总价格为$1000\times 1+100\times 6=1600$日元。
由于产品总额少于2000日元，运费为500日元。
因此，Takahashi将支付的金额为$1600+500=2100$日元。

样例输入2

3 2000 500
1000 1
100 6
5000 1

样例输出2

6600

产品的总价格为$1000\times 1+100\times 6+5000\times 1=6600$日元。
由于产品总额不