n, k = map(int, input().split())
k -= 1  # Convert to 0-based index
a = list(map(int, input().split()))

sum_left = 0
current_min = a[k]
sum_left = current_min
for i in range(k-1, -1, -1):
    current_min = min(current_min, a[i])
    sum_left += current_min

sum_right = 0
current_min = a[k]
sum_right = current_min
for i in range(k+1, n):
    current_min = min(current_min, a[i])
    sum_right += current_min

print(max(sum_left, sum_right))