#include <bits/stdc++.h>
#define REP(i, start, end) for (int i=start, i##Len=(end); i < i##Len; ++i)
using ll = int64_t;


int main() {
    using namespace std;
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(20);

    int N, K;
    cin >> N >> K;
    vector<ll> X(N+2), A(N+2, 0);

    REP(i, 1, N+1) cin >> X[i];
    REP(i, 1, N+1) cin >> A[i];
    X[0] = LLONG_MIN;
    X[N+1] = LLONG_MAX;

    int li = K, ri = K, prev_li = -1, prev_ri = -1;
    ll l = X[li] - A[li], r = X[ri] + A[ri];

    while (prev_li != li || prev_ri != ri) {
        prev_li = li, prev_ri = ri;
        while (l <= X[li-1]) {
            l = min(l, X[--li]-A[li]);
            r = max(r, X[li]+A[li]);
        }
        while (X[ri+1] <= r) {
            l = min(l, X[++ri]-A[ri]);
            r = max(r, X[ri]+A[ri]);
        }
    }

    cout << ri-li+1 << endl;

    return 0;
}