import strutils,sequtils,deques
var
    N,K : int
(N, K) = stdin.readline.split.map(parseInt)
var
    X = stdin.readline.split.map(parseBiggestInt)
    A = stdin.readline.split.map(parseBiggestInt)
    u : bool = true
    que = initDeque[int](1024)
    lx,rx,lx2,rx2 : int64
    ln,rn : int
    used : array[100010, bool]
    ans : int = 1
    
K -= 1
lx = X[K]
rx = X[K]
ln = K
rn = K
lx2 = X[K]
rx2 = X[K]
que.addLast(K)

while que.len > 0:
    u = false
    while que.len > 0:
        var p = que.popFirst
        lx2 = min(lx2, X[p] - A[p])
        rx2 = max(rx2, X[p] + A[p])
    for n in countdown(ln - 1, 0):
        if X[n] >= lx2:
            que.addLast(n)
            ln = n
            ans += 1
        else:
            break
    lx = lx2
    for n in (rn + 1) .. <N:
        if X[n] <= rx2:
            que.addLast(n)
            rn = n
            ans += 1
        else:
            break
    rx = rx2

echo ans