#yuki823

mod=10**9+7
def f(x):
 return x*(x+1)/2%mod

n,k=map(int,raw_input().split())
a=f(n)
b=f(n-1)*f(k-1)%mod
for i in xrange(k):
 a*=(n-i-1)%mod
 a=a%mod
for i in xrange(k-2):
 b*=(n-i-2)%mod
 b=b%mod
print (a+b)%mod