#include <bits/stdc++.h>
#define REP(i, n) for(int i = 0;i < n;i++)
#define VSORT(v) sort(v.begin(), v.end())
#define VRSORT(v) sort(v.rbegin(), v.rend())
#define ll long long
using namespace std;
typedef pair<int, int> P;
typedef pair<ll, ll> LP;
typedef pair<int, P> PP;
typedef pair<ll, LP> LPP;
typedef vector<unsigned int>vec;
typedef vector<vec> mat;
typedef vector<vector<int>> Graph;

const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
const int INF = 1000000000;
const ll LINF = 1000000000000000000;//1e18
const ll  MOD = 1000000007;
const double PI = acos(-1.0);
const double EPS = 1e-10;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline void add(T &a, T b){a = ((a+b) % MOD + MOD) % MOD;};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    int N,K;
    cin >> N >> K;
    vector<ll> X(N), A(N);
    REP(i,N) cin >> X[i];
    REP(i,N) cin >> A[i];
    int ans = 1;
    for(int i=K-1;i<N;i++){
        if(i == N-1) break;
        else{
            if(X[i+1] - X[i] <= A[i]) ans++;
            else break;
        }
    }
    for(int i=K-1;i>=0;i--){
        if(i == N-1) break;
        else{
            if(X[i] - X[i-1] <= A[i]) ans++;
            else break;
        }
    }
    cout << ans << endl;
}