暂无测试数据。

英文题面

Bessie is a hungry cow. Each day, for dinner, if there is a haybale in the barn,she will eat one haybale. Farmer John does not want Bessie to starve, so some days he sends a delivery of haybales, which arrive in the morning (before dinner). In particular, on day $d_i$, Farmer John sends a delivery of $b_i$ haybales ($1\leq d_i \leq 10^{14}$, $1 \leq b_i \leq 10^9$).

Compute the total number of haybales Bessie will eat during the first $T$ days.

译文

贝茜是一头饥饿牛。对于每天的晚餐，如果谷仓里有一捆干草，她就会吃一捆。农民约翰不想让贝茜挨饿，所以有时他送很多捆干草，早上(晚饭前)送到。特别地，在第 $d_i$ 天，农夫约翰送了 $b_i$ 捆干草($1\leq d_i \leq 10^{14}$， $1\leq b_i \leq 10^9$)。

计算贝茜在前 $T$ 天会吃掉的干草总数。

输入格式

The first line contains $N$ and $T$ ($1 \le N \le 10^5$, $1 \le T \le 10^{14}$).

The next $N$ lines each contain $d_i$ and $b_i$. It is additionally guaranteed that $1\le d_1 < d_2 < \dots < d_N\le T$.

第一行包含 $N$ 和 $T$ ($1 \le N \le 10^5$， $1 \le T \le 10^{14}$)。

接下来的 $N$ 行每个包含 $d_i$ 和 $b_i$。另外还保证 $1\le d_1 < d_2 < \dots < d_N\le T$。

输出格式

Output the number of haybales that Bessie will eat during the first $T$ days.

输出贝茜在前 $T$ 天会吃的干草数量。

数据范围

• Inputs 4-7: $T\leq 10^5$
• Inputs 8-13: No additional constraints.

1 5
1 2

2

2 5
1 2
5 10

3

2 5
1 10
5 10

5