A7959 | 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.

The first line contains two integers $n$ and $d$ ( $1<=n<=1000,1<=d<=10^{9}$ ) — 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 $10^{9}$ .

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