#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n, k, ans = 0;
    cin >> n >> k;
    bool flag = 1;
    pair<long long, long long> p[n];
    for (int i = 0; i < n; i++) cin >> p[i].first;
    for (int i = 0; i < n; i++) cin >> p[i].second;
    //  正方向への探索
    for (int i = k-1; flag && i < n-1; i++) {
        if (p[i].second + p[i].first >= p[i+1].first) ans++;
        else flag = 0;
        
    }
    flag = 1;
    for (int i = k-1; flag && i > 0; i--) {
        if (p[i].first - p[i].second <= p[i-1].first) ans++;
        else flag = 0;
    }
    cout << ans+1 << endl;
    return 0;
}