import sys

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 18
MOD = 10 ** 9 + 7
EPS = 10 ** -10

N, K = MAP()
K -= 1
X = LIST()
A = LIST()

ok = [0] * N
ok[K] = 1
lmx = X[K] - A[K]
for i in range(K-1, -1, -1):
    if lmx <= X[i]:
        lmx = min(lmx, X[i]-A[i])
        ok[i] = 1
    else:
        break
rmx = X[K] + A[K]
for i in range(K+1, N):
    if rmx >= X[i]:
        rmx = max(rmx, X[i]+A[i])
        ok[i] = 1
    else:
        break
ans = sum(ok)
print(ans)