INF = 10 ** 7
import sys
input = sys.stdin.readline
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)

def main():
    n,k = map(int,input().split())
    X = list(map(int,input().split()))
    A = list(map(int,input().split()))

    k -= 1
    l,r = k,k
    lM,rM = X[k] - A[k],X[k] + A[k]
    while l >= 1 or r < n - 1:
        if r + 1 < n and X[r + 1] <= rM:
            r += 1
            rM = max(rM,X[r] + A[r])
            lM = min(lM,X[r] - A[r])
        elif l - 1 >= 0 and X[l - 1] >= lM:
            l -= 1
            rM = max(rM,X[l] + A[l])
            lM = min(lM,X[l] - A[l])
        else:
            break
    
    print(r - l + 1)

if __name__ == '__main__':
    main()