import sys

def solve():
    N, K = map(int, sys.stdin.readline().split())
    A = list(map(int, sys.stdin.readline().split()))

    k_idx = K - 1  # Convert to 0-indexed

    if A[k_idx] == 0:
        print(0)
        return

    max_coins = A[k_idx]

    # Explore to the left
    for i in range(k_idx - 1, -1, -1):
        if A[i] == 0:
            break
        max_coins += A[i]
        if A[i] == 1:
            break
            
    # Explore to the right
    for i in range(k_idx + 1, N):
        if A[i] == 0:
            break
        max_coins += A[i]
        if A[i] == 1:
            break
            
    print(max_coins)

if __name__ == '__main__':
    solve()