import sys
input = sys.stdin.readline

N, K = map(int, input().split())
K -= 1
A = list(map(int, input().split()))

for i in range(K+1, N):
    if A[i]<=1:
        r = i
        break
else:
    r = N-1

for i in range(K-1, -1, -1):
    if A[i]<=1:
        l = i
        break
else:
    l = 0

if A[K]==0:
    print(0)
elif A[K]==1:
    print(max(sum(A[l:K+1]), sum(A[K:r+1])))
else:
    print(sum(A[l:r+1]))