#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);
    vector<ll> a(n),b(n);
    rep(i,0,n)scanf("%lld",&a[i]);
    rep(i,0,n)scanf("%lld",&b[i]);
    bool fl[100010]={}; fl[k-1]=1;
    ll maxx=0;
    rrep(i,k-2,-1){
        if(a[i+1]-a[i]<=max(maxx,b[i+1])){
            fl[i]=1; chmax(maxx,b[i+1]);
        }
        else break;
        maxx-=a[i+1]-a[i];
    }
    maxx=0;
    rep(i,k,n){
        if(a[i]-a[i-1]<=max(maxx,b[i-1])){
            fl[i]=1; chmax(maxx,b[i-1]);
        }
        else break;
        maxx-=a[i]-a[i-1];
    }
    int cnt=0;
    rep(i,0,n)if(fl[i])cnt++;
    printf("%d\n",cnt);
    return 0;
}