#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
constexpr int INF = 1001001001;
// constexpr int mod = 1000000007;
constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

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

    int N, K;
    cin >> N >> K;
    --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];

    int i = K - 1, j = K + 1;
    int l = lower_bound(begin(X), end(X), X[K] - A[K]) - begin(X);
    int r = upper_bound(begin(X), end(X), X[K] + A[K]) - begin(X);
    while(l <= i || j < r){
        if(l <= i){
            chmin<int>(l, lower_bound(begin(X), end(X), X[i] - A[i]) - begin(X));
            chmax<int>(r, upper_bound(begin(X), end(X), X[i] + A[i]) - begin(X));
            --i;
        }
        if(j < r){
            chmin<int>(l, lower_bound(begin(X), end(X), X[j] - A[j]) - begin(X));
            chmax<int>(r, upper_bound(begin(X), end(X), X[j] + A[j]) - begin(X));
            ++j;
        }
    }

    cout << r - l << endl;

    return 0;
}