import sys
n,k=map(int,input().split())
a=list(map(int,sys.stdin.readline().split()))
a.sort()
res=0
i=n-1
while i>0:
    if a[i]-a[i-1]<=k:
        res+=a[i]*a[i-1]
        i-=2
    else:
        i-=1
print(res)