#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
//-------------------------------------------------------

int N,K;
ll X[101010];
ll A[101010];

set<pair<ll,ll>> S;
queue<int> Q;

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>K;
	FOR(i,N) {
		cin>>X[i];
		if(i==K-1) {
			Q.push(i);
		}
		else {
			S.insert({X[i],i});
		}
	}
	FOR(i,N) cin>>A[i];
	
	int ret=0;
	while(Q.size()) {
		x=Q.front();
		Q.pop();
		ret++;
		ll y=X[x]-A[x];
		while(1) {
			auto it=S.lower_bound({y,0});
			if(it==S.end()) break;
			if(it->first>X[x]+A[x]) break;
			Q.push(it->second);
			S.erase(it);
		}
		
		
	}
	
	
	cout<<ret<<endl;
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}