#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];
    }
    int ans = 1;
    //左方向
    int leftest = X[K] - A[K];
    for (int i = K - 1; i >= 0; --i) {
        if (leftest <= X[i]) {
            ans++;
            leftest = min(leftest, X[i] - A[i]);
        } else break;
    }
    //右方向
    int rightest = X[K] + A[K];
    for (int i = K + 1; i < N; ++i) {
        if (X[i] <= rightest) {
            ans++;
            rightest = max(rightest, X[i] + A[i]);
        } else break;
    }
    cout << ans << endl;
    return 0;
}