; タイプ別設定 Ver1
; Monokai for Sakura Editor (C/C++)
; cpp_monokai.ini
;
;  Created on: 2015/06/13
;      Author: KeitetsuWorks

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[TypeEx]
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szKeywordFile[2]=cpp_kw2_keywords.kwd
szKeywordFile[3]=cpp_kw3_functions.kwd
szKeyword[1]=cpp_kw1_datatypes
szKeyword[2]=cpp_kw2_keywords
szKeyword[3]=cpp_kw3_functions

[Info]
szVersion=2.2.0.1
vStructureVersion=166



### FIXED CODE ###

N,K = map(int,input().split())

mod = 10**9+7
ans = 0

for i in range(K,N+2):
    min = (0+i-1)*i//2
    max = (N+N-i+1)*i//2
    
    ans += (max-min+1)%mod
    
print(ans%mod)