#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;

//template
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(a);i>(b);i--)
#define ALL(v) (v).begin(),(v).end()
typedef long long int ll; typedef pair<ll, ll> P;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<typename A,size_t N,typename T>void Fill(A(&array)[N],const T &val){fill((T*)array, (T*)(array+N), val);}
const int inf = INT_MAX / 2; const ll INF = LLONG_MAX / 2;
//template end


int main(){
    int n,k; scanf("%d%d",&n,&k); k--;
    vector<ll> x(n),a(n);
    rep(i,0,n)scanf("%lld",&x[i]);
    rep(i,0,n)scanf("%lld",&a[i]);
    int lb=k,rb=k;
    ll lv=x[k]-a[k],rv=x[k]+a[k];
    bool fl=true;
    while(fl){
        fl=false;
        if(0<lb&&lv<=x[lb-1]){
            lb--;
            chmin(lv,x[lb]-a[lb]);
            chmax(rv,x[lb]+a[lb]);
            fl=true;
        }
        if(rb<n-1&&x[rb+1]<=rv){
            rb++;
            chmin(lv,x[rb]-a[rb]);
            chmax(rv,x[rb]+a[rb]);
            fl=true;
        }
    }
    printf("%d\n",rb-lb+1);
    return 0;
}