#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;
typedef pair<ll, P> P3;
typedef pair<P, P> PP;
constexpr ll MOD = ll(1e9 + 7);
constexpr int IINF = INT_MAX;
constexpr ll LLINF = LLONG_MAX;
constexpr int MAX_N = int(1e5) + 5;
constexpr double EPS = 1e-9;
constexpr int di[] = {0, 1, 0, -1}, dj[] = {1, 0, -1, 0};
#define REP(i, n) for (int i = 0; i < n; i++)
#define REPR(i, n) for (int i = n; i >= 0; i--)
#define SORT(v) sort((v).begin(), (v).end())
#define SORTR(v) sort((v).rbegin(), (v).rend())
#define ALL(v) (v).begin(), (v).end()


int main() {
    ll n, k;
    cin >> n >> k;
    vector<ll> x(n), a(n);
    for(int i=0;i<n;i++){
        cin >> x[i];
    }
    for(int i=0;i<n;i++){
        cin >> a[i];
    }
    ll l = k-1, r = k-1;
    for(ll pos = x[r]; r<n-1; r++){
        pos = max(pos, x[r]+a[r]);
        if(x[r+1] > pos) break;
    }
    for(ll pos = x[l]; l>0; l--){
        pos = min(pos, x[l]-a[l]);
        if(x[l-1] < pos) break;
    }
    cout << r-l+1 << endl;
    return 0;
}