def main():
    from math import sqrt,sin,cos,tan,ceil,radians,floor,gcd,exp,log,log10,log2,factorial,fsum
    from heapq import heapify, heappop, heappush
    from bisect import bisect_left, bisect_right
    from copy import deepcopy
    import copy
    import random
    from collections import deque,Counter,defaultdict
    from itertools import permutations,combinations
    from decimal import Decimal,ROUND_HALF_UP
    #tmp = Decimal(mid).quantize(Decimal('0'), rounding=ROUND_HALF_UP)
    from functools import lru_cache, reduce
    #@lru_cache(maxsize=None)
    from operator import add,sub,mul,xor,and_,or_,itemgetter
    INF = 10**18
    mod1 = 10**9+7
    mod2 = 998244353
    
    #DecimalならPython
    
    
    '''
    
    
    
    '''
    
    N,K = map(int, input().split())
    A = list(map(int, input().split()))
    
    rCk = [-1]*(N+1)
    rCk[0] = 1
    for i in range(1,N+1):
        r = K+i
        rCk[i] = rCk[i-1]*r*pow(r-K,mod1-2,mod1)
        rCk[i] %= mod1
    
    ans = 0
    for i in range(1,N+1):
        ans += rCk[i-1]*rCk[N-i]*A[i-1]
        ans %= mod1
    
    print(ans)
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
if __name__ == '__main__':
    main()