102970: [Atcoder]ABC297 A - Double Click

Problem Statement

Takahashi turned on a computer at time $0$ and clicked the mouse $N$ times. The $i$-th $(1 \le i \le N)$ click was at time $T_i$.

If he consecutively clicked the mouse at time $x_1$ and time $x_2$ (where $x_1 < x_2$), a double click is said to be fired at time $x_2$ if and only if $x_2 - x_1 \le D$.

What time was a double click fired for the first time? If no double click was fired, print -1 instead.

Constraints

• $1 \le N \le 100$
• $1 \le D \le 10^9$
• $1 \le T_i \le 10^9(1 \le i \le N)$
• $T_i < T_{i+1}(1 \le i \le N-1)$
• All values in the input are integers.

Input

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

$N$ $D$
$T_1$ $T_2$ $\dots$ $T_N$

Output

If at least one double click was fired, print the time of the first such event; otherwise, print -1.

Sample Input 1

4 500
300 900 1300 1700

Sample Output 1

1300

Takahashi clicked the mouse at time $900$ and $1300$. Since $1300 - 900 \le 500$, a double click was fired at time $1300$.

A double click had not been fired before time $1300$, so $1300$ should be printed.

Sample Input 2

5 99
100 200 300 400 500

Sample Output 2

-1

No double click was fired, so print -1.

Sample Input 3

4 500
100 600 1100 1600

Sample Output 3

600

If multiple double clicks were fired, be sure to print only the first such event.

问题描述

高桥在时间0打开电脑并点击鼠标N次。第i次点击（1≤i≤N）发生的时间为T_i。

如果他在时间x₁和时间x₂（其中x₁＜x₂）连续点击鼠标，那么当且仅当x₂ - x₁ ≤ D时，称在时间x₂触发了双击。

第一次触发双击是什么时候？如果没有触发双击，则打印-1。

约束

• 1≤N≤100
• 1≤D≤10⁹
• 1≤T_i≤10⁹（1≤i≤N）
• T_i＜T_i+1（1≤i≤N-1）
• 输入中的所有值都是整数。

输入

输入通过标准输入给出，如下所示：

$N$ $D$
$T_1$ $T_2$ $\dots$ $T_N$

输出

如果至少触发了一次双击，请打印第一次这样的事件的时间；否则，打印-1。

样例输入1

4 500
300 900 1300 1700

样例输出1

1300

高桥在时间900和1300点击了鼠标。由于1300 - 900 ≤ 500，因此在时间1300触发了双击。

在时间1300之前没有触发过双击，因此应该打印1300。

样例输入2

5 99
100 200 300 400 500

样例输出2

-1

没有触发双击，所以打印-1。

样例输入3

4 500
100 600 1100 1600

样例输出3

600

如果有多个触发的双击，务必只打印第一次这样的事件。