#include<bits/stdc++.h>
using namespace std;
int n,m,a[200005],b[200005],sum;
bool mp1[20005][20005];
short w[2][2]={0,1,1,0};
struct node{
	int x,y;
};
deque <node> q;
void bfs(int X,int Y){
	node e;
	e.x=X,e.y=Y;
	q.push_back(e);
	while(q.size()){
		if(q.front().y==m&&mp1[q.front().x][q.front().y]){
			sum++,mp1[q.front().x][q.front().y]=0;
//			cout<<q.front().x<<" "<<q.front().y<<endl;
		}
		for(int i=0;i<2;i++){
			node ee;
			ee.x=q.front().x+w[i][0],ee.y=q.front().y+w[i][1];
			if(ee.x>=1&&ee.x<=n&&ee.y>=1&&ee.y<=m&&mp1[ee.x][ee.y]){
				q.push_back(ee);
			}
		}
		q.pop_front();
	}
}
int main(){
	freopen("expansion.in","r",stdin);
	freopen("expansion.out","w",stdout);
	cin>>n>>m;
	for(int i=1;i<=n;i++){
		cin>>a[i];
	}
	for(int i=1;i<=m;i++){
		cin>>b[i];
	}
	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			if(a[i]+b[j]>=0){
				mp1[i][j]=1;
			}
			else{
				mp1[i][j]=0;
			}
//			cout<<mp1[i][j]<<" ";
		}
//		cout<<endl;
	}
	for(int i=1;i<=n;i++){
		if(mp1[i][1]){
//			cout<<i<<endl;
			bfs(i,1);
		}
		for(int j=i+1;j<=n;j++){
			if(a[j]+b[m]>=0){
				mp1[j][m]=1;
			}
		}
	}
//	cout<<n<<" "<<m<<endl;
	cout<<sum;
	return 0;
}