#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep3(i, l, n) for (int i = l; i < (n); ++i)
#define sz(v) (int)v.size()
#define inf (int)(1e9+7)
#define abs(x) (x >= 0 ? x : -(x))
#define ceil(a, b) a / b + !!(a % b)
ll pow(ll a, int b) { return b ? pow(a * a, b / 2) * (b % 2 ? a : 1) : 1; }
template<typename T> T gcd(T a, T b) { if (b == 0) return a; return gcd(b, a % b); }




int main() {
    int n, k;
    cin >> n >> k;
    vector<ll> x(n), a(n);
    k--;
    rep(i, n) cin >> x[i];
    rep(i, n) cin >> a[i];
    
    ll l = x[k] - a[k], r = x[k] + a[k];
    // cout << l << " " << r << endl;
    
    int lid = k, rid = k;
    int c = 0;
    while (c++ < n) {
        rep(i, 2) {
            int it;
            if (i == 0) {
                it = (int)(upper_bound(all(x), r) - x.begin());
                it--;
            } else {
                it = (int)(lower_bound(all(x), l) - x.begin());
            }
            
            {
                
                // cout << it << " " << lid << " " << rid << endl;
                rep3(i, it, lid) {
                    l = min(l, x[i] - a[i]);
                    r = max(r, x[i] + a[i]);
                    
                }
                
                rep3(i, rid + 1, it + 1) {
                    l = min(l, x[i] - a[i]);
                    r = max(r, x[i] + a[i]);
                    
                }
                
                lid = min(lid, it);
                rid = max(rid, it);
            }
            // cout << l << " " << r << endl;
        }
        
    }
    
    
    
    // cout << lid << " " << rid << endl;
    cout << rid - lid + 1 << endl;
}