import math
import queue
 
def readInt():
	return int(input())
 
def readInts():
	return list(map(int, input().split()))
 
def readChars():
	return input().split()

x = readInts()
n = x[0]
k = x[1]

def ts(l):
	return int((l*(l-1))/2)

def ts2(l):
	return int(l*(n+n-(l-1))/2)

s = 0

for i in range(k,n+2):
	s += ts2(i)+1-ts(i)

print(s%(1000000007))