import sequtils, strutils, algorithm, math, future, sets, tables, hashes, intsets
let read = iterator : string {.closure.} = (while true: (for s in stdin.readLine.split : yield s))


var
    n,k = read().parseint
    a = newseqwith(n, read().parseint)

var
    l = 0
    r = n - 1

for i in 0 ..< n:
    if a[i] <= 1:
        if i < k:
            l = i
        else:
            r = i
            break

if a[k - 1] == 0:
    echo 0
    quit()

if a[k - 1] == 1:
    echo max(a[l .. k].sum, a[k .. r].sum)
    quit()

echo a[l .. r].sum