#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <ios>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <forward_list>
#include <random>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <unordered_map>
#include <unordered_set>
#endif

#define F first
#define S second
#define MP make_pair
#define pb push_back
#define all(a) a.begin(), a.end()
#define lcm( a, b ) (a)/__gcd((a),(b))*(b)
#define endl '\n'

using namespace std;

typedef long long LL;
typedef pair< int, int > P;
typedef pair< LL, LL > LP;
typedef pair< int, P > iP;
typedef pair< P, P > PP;

static const int INF = INT_MAX;
static const LL LINF = LLONG_MAX;
static const int MIN = INT_MIN;
static const LL LMIN = LLONG_MIN;
static const int MOD = 1000000007;
static const int SIZE = 100005;

const int dx[] = {0, -1, 1, 0};
const int dy[] = {-1, 0, 0, 1};

vector< int > Div( int n ) {
    vector< int > ret;
    for( int i = 1; i * i <= n; ++i ) {
        if( n % i == 0 ) {
            ret.pb( i );

            if( i * i != n ) ret.pb( n / i );
        }
    }
    sort( all( ret ) );
    return ret;
}

void dfs( int pos );

vector< LL > v;
int l, r;
int n, k;
LL a[SIZE];
bool dist[SIZE];

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

    cin >> n >> k;
    for( int i = 0; i < n; ++i ) {
        LL a;
        cin >> a;
        v.pb( a );

    }
    for( int i = 0; i < n; ++i ) {
        cin >> a[i];

    }

    l = r = k - 1;
    dfs( k - 1 );
    cout << r - l + 1 << endl;

    return 0;
}

void dfs( int pos ) {
    if( pos > n - 1 || pos < 0 ) {
        return;

    }

    LL large = v[pos] - a[pos];
    int left = lower_bound( v.begin(), v.begin() + pos, large ) - v.begin();
    large = v[pos] + a[pos];
    int right = upper_bound( v.begin() + pos, v.end(), large ) - v.begin() - 1;
    l = min( l, left );
    r = max( r, right );
    if( !dist[left] ) {
        dist[left] = true;
        dfs( left );

    }

    if( !dist[right] ) {
        dist[right] = true;
        dfs( right );

    }
    return;

}