from collections import deque, defaultdict, Counter
from bisect import bisect_left, bisect_right
from itertools import permutations, combinations
from heapq import heappop, heappush
import math, sys
# input = sys.stdin.readline
_int = lambda x: int(x)-1
MOD = 998244353 #10**9+7
INF = 1<<60
Yes, No = "Yes", "No"

N, K = map(int, input().split())
A = list(map(int, input().split()))
while A and len(A) > K:
    if A[-1] < 0: A.pop()
    else: break
N = len(A)
cum = [0]
for a in A: cum.append(cum[-1]+a)
ans = 0
cur = N-1
for i in reversed(range(1, K)):
    cnt = A[cur]
    cur -= 1
    while A[cur] >= 0 and i <= cur:
        cnt += A[cur]
        cur -= 1
    ans += cnt*(i+1)
ans += cum[cur+1]
print(ans)