#include<bits/stdc++.h>

#define int long long
using namespace std;
#define rep(i, n) for(int i=0;i<(n);++i)
typedef pair<int, int> pii;
const int INF = 1l << 60;
#define u_b upper_bound
#define l_b lower_bound

int N, K;
int X[100100];
int A[100100];

signed main() {
    cin >> N >> K;
    --K;
    rep(i, N) {
        cin >> X[i];
    }
    rep(i, N) {
        cin >> A[i];
    }
    //左方向
    int leftest = X[K] - A[K];
    int left_right = X[K];
    int left = 0;
    for (int i = K - 1; i >= 0; --i) {
        if (leftest <= X[i]) {
            left++;
            leftest = min(leftest, X[i] - A[i]);
            left_right = max(left_right, X[i] + A[i]);
        } else break;
    }
    //右方向
    int right = 0;
    int rightest = X[K] + A[K];
    int right_left = X[K];
    for (int i = K + 1; i < N; ++i) {
        if (X[i] <= rightest) {
            right++;
            rightest = max(rightest, X[i] + A[i]);
            right_left = min(right_left, X[i] - A[i]);
        } else break;
    }
    leftest = min(leftest, right_left);
    rightest = max(rightest, left_right);
    while (1) {
        if (K - left == 0) {
            if (K + right == N - 1) {
                break;
            }
            if (X[K + right + 1] <= rightest) {
                right++;
                rightest = max(rightest, X[K + right] + A[K + right]);
                continue;
            } else break;
        } else {
            if (K + right == N - 1) {
                if (leftest <= X[K - left - 1]) {
                    left++;
                    leftest = min(leftest, X[K - left] - A[K - left]);
                    continue;
                } else break;
            } else {
                if (X[K + right + 1] <= rightest) {
                    right++;
                    rightest = max(rightest, X[K + right] + A[K + right]);
                    leftest = min(leftest, X[K + right] - A[K + right]);
                    continue;
                }
                if (leftest <= X[K - left - 1]) {
                    left++;
                    leftest = min(leftest, X[K - left] - A[K - left]);
                    rightest = max(rightest, X[K - left] + A[K - left]);
                    continue;
                }
                break;
            }
        }
    }
    cout << left + right + 1 << endl;
    return 0;
}