CF32A.Reconnaissance

According to the regulations of Berland's army, a reconnaissance unit should consist of exactly two soldiers. Since these two soldiers shouldn't differ much, their heights can differ by at most d centimeters. Captain Bob has n soldiers in his detachment. Their heights are _a_1, _a_2, ..., a__n centimeters. Some soldiers are of the same height. Bob wants to know, how many ways exist to form a reconnaissance unit of two soldiers from his detachment.

Ways (1, 2) and (2, 1) should be regarded as different.

根据贝尔兰军队的规定，一支侦察小队必须恰好由两名士兵组成。由于这两名士兵的身高不应相差太大，因此他们的身高差最多为 $d$ 厘米。鲍勃上尉的分队中有 $n$ 名士兵，他们的身高分别为 $a_1,\,a_2,\,\dots,\,a_n$ 厘米。部分士兵身高相同。鲍勃想知道，从他的分队中选出两名士兵组成一支侦察小队，共有多少种方式。

方式 $(1,\,2)$ 和 $(2,\,1)$ 应被视为不同的方式。

The first line contains two integers n and d (1 ≤ n ≤ 1000, 1 ≤ d ≤ 109) — amount of soldiers in Bob's detachment and the maximum allowed height difference respectively. The second line contains n space-separated integers — heights of all the soldiers in Bob's detachment. These numbers don't exceed 109.

第一行包含两个整数 $n$ 和 $d$（$1 \leq n \leq 1000$，$1 \leq d \leq 10^9$）—— 分别表示鲍勃部队中的士兵人数和允许的最大身高差。
第二行包含 $n$ 个用空格分隔的整数——表示鲍勃部队中所有士兵的身高。这些数值均不超过 $10^9$。

Output one number — amount of ways to form a reconnaissance unit of two soldiers, whose height difference doesn't exceed d.

输出一个数字——组成一支侦察小队（由两名士兵组成）的方案数，要求这两名士兵的身高差不超过 $d$。