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

    if A[K] == 0:
        return 0

    if A[K] == 1:
        L = 1
        i = K - 1
        while i >= 0:
            if A[i] == 0:
                break
            if A[i] == 1:
                L += 1
                break
            L += A[i]
            i -= 1
        R = 1
        i = K + 1
        while i < N:
            if A[i] == 0:
                break
            if A[i] == 1:
                R += 1
                break
            R += A[i]
            i += 1
        return max(L, R)

    res = A[K]
    i = K - 1
    while i >= 0:
        if A[i] == 0:
            break
        if A[i] == 1:
            res += 1
            break
        res += A[i]
        i -= 1
    i = K + 1
    while i < N:
        if A[i] == 0:
            break
        if A[i] == 1:
            res += 1
            break
        res += A[i]
        i += 1
    return res


print(main())