#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using ll =  long long ;
using P = pair<int,int> ;
const int INF = 1e9;
const int MOD = 1000000007;

int main(){
    int n,k;
    cin >> n >> k;
    --k;
    vector<ll> x(n),a(n);
    rep(i,n) cin >> x[i];
    rep(i,n) cin >> a[i];
    int i = k-1,j = k+1;
    int cnt = 1;
    ll mn = x[k] - a[k];
    ll mx = x[k] + a[k];
    while(1){
        bool update = false;
        if(i >= 0){
            if(mn <= x[i]){
                cnt ++;
                mn = min(mn,x[i]-a[i]);
                mx = max(mx,a[i]+x[i]);
                --i;
                update = true;
            }
        }
        if(j < n){
            if(x[j] <= mx){
                cnt ++;
                mn = min(mn,x[j]-a[j]);
                mx = max(mx,a[j]+x[j]);
                ++j;
                update = true;
            }
        }
        if(!update) break;
    }
    cout << cnt << endl;
    return 0;
}