#include <bits/stdc++.h>
using namespace std;

int main() {
    long long N, K;
    cin >> N >> K;
    long long X[N], A[N];
    for (size_t i = 0; i < N; i++) {
        cin >> X[i];
    }
    for (size_t i = 0; i < N; i++) {
        cin >> A[i];
    }
    long long L = X[K - 1] - A[K - 1], R = X[K - 1] + A[K - 1];
    long long L_index = K - 1, R_index = K - 1;
    while (true) {
        if (0 <= L_index - 1) {
            if (L <= X[L_index - 1]) {
                L_index--;
                L = min(L, X[L_index] - A[L_index]);
                R = max(R, X[L_index] + A[L_index]);
            }
        }
        if (R_index + 1 < N) {
            if (X[R_index + 1] <= R) {
                R_index++;
                L = min(L, X[R_index] - A[R_index]);
                R = max(R, X[R_index] + A[R_index]);
            }
        }
        break;
    }
    cout << R_index - L_index + 1 << endl;
}