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

if A[K] == 0:
    exit(print(0))

# 0 or 1 にたどりつくまで左右に探索
left = 0
for i in range(K - 1, -1, -1):
    if A[i] == 0:
        break
    if A[i] == 1:
        left += 1
        break
    left += A[i]

right = 0
for i in range(K + 1, N):
    if A[i] == 0:
        break
    if A[i] == 1:
        right += 1
        break
    right += A[i]

if A[K] == 1: # 左右どちらかだけいける
    ans = max(left, right) + 1
else:
    ans = left + right + A[K]

print(ans)