a = 1
x,y = map(int, input().split())
lisX = list(map(int, input().split()))
lisA = list(map(int, input().split()))



for i in range(x//2):
    t = lisX[y-1+i] + lisA[y-1+i]
    s = lisX[y-1-i] - lisA[y-1-i]
        
    if lisX[y-2-i] >= s:
        a += 1
        
    if lisX[y+i] <= t:
        a += 1
        
print(a)