# https://codeforces.com/contest/622/problem/F

n,K=map(int,input().split())
mod=10**9+7

FACT=[1]*(10+10**6)
F=[0]*(10+10**6)
for i in range(1,10+10**6):
    FACT[i]=FACT[i-1]*i%mod
    F[i]=(F[i-1]+pow(i,K,mod))%mod

FACT_INV=[0]*(10+10**6)
FACT_INV[-1]=pow(FACT[-1],mod-2,mod)
for i in range(10+10**6-1,0,-1):
    FACT_INV[i-1]=FACT_INV[i]*i%mod


T=K+2
def powKsum(x):
    if x<=T:
        return F[x]
    ANS=0
    PI=1

    for i in range(1,K+3):
        PI=PI*(x-i)%mod
        if (T-i)%2==0:
            ANS+=F[i]*FACT_INV[T-i]*FACT_INV[i-1]*pow(x-i,mod-2,mod)
        else:
            ANS-=F[i]*FACT_INV[T-i]*FACT_INV[i-1]*pow(x-i,mod-2,mod)
        ANS%=mod
            
    return ANS*PI%mod

print(powKsum(n))