#include <bits/stdc++.h>
using namespace std;
#define REP(i,a) for(int i = 0; i < (a); i++)
#define ALL(a) (a).begin(),(a).end()
typedef long long ll;
typedef pair<int, int> P;
const int INF = 1e9;
const int MOD = 1e9 + 7;

signed main(){
    int n,k;
    cin >> n >> k;
    k--;
    ll x[n],a[n];
    REP(i,n){
        cin >> x[i];
    }
    REP(i,n){
        cin >> a[i];
    }
    int ans = 1;
    for(int i = k; i < n - 1; i++){
        if(x[i] + a[i] < x[i + 1]){
            break;
        }
        ans++;
    }
    for(int i = k; i > 0; i--){
        if(x[i] - a[i] > x[i - 1]){
            break;
        }
        ans++;
    }
    cout << ans << endl;
}