#include<bits/stdc++.h>
using namespace std;
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define INF 1000000000
#define mod 1000000007
using ll=long long;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int n,k;cin>>n>>k;k--;
    ll x[n],a[n];
    rep(i,n) cin>>x[i];
    rep(i,n) cin>>a[i];
    int l[n],r[n];

    rep(i,n){
        auto ite=lower_bound(x,x+n,x[i]-a[i]);
        l[i]=ite-x;
        ite=lower_bound(x,x+n,x[i]+a[i]+1);
        ite=prev(ite);
        r[i]=ite-x;
    }

    int nl=k,nr=k;
    queue<int> que;
    que.push(k);
    int ans=1;
    while(!que.empty()){
        int idx=que.front();que.pop();
        while(l[idx]<nl){
            ans++;
            que.push(nl-1);
            nl--;
        }
        while(nr<r[idx]){
            ans++;
            que.push(nr+1);
            nr++;
        }
    }

    // cout<<nl<<" "<<nr<<endl;
    cout<<ans<<endl;
    return 0;
}