#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    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 idL = K, idR = K;
    ll vL = X[K] - A[K], vR = X[K] + A[K];
    while(true) {
        if(0 <= idL - 1 && vL <= X[idL - 1]) {
            idL--;
            vL = min(vL, X[idL] - A[idL]);
            vR = max(vR, X[idL] + A[idL]);
        } else if(idR + 1 < N && X[idR + 1] <= vR) {
            idR++;
            vL = min(vL, X[idR] - A[idR]);
            vR = max(vR, X[idR] + A[idR]);
        } else break;
    }

    cout << idR - idL + 1 << endl;
}