> #include<iostream>
> using namespace std;
> int si[1000],fi[1000],sumn[1000],ans=-999999,n;
> void dfs(int p,int ssum,int fsum,int sum)
> {
> 	if(p>n)
> 	{
> 		if(sum>ans)
> 			ans=sum;
> 		return ;
> 	}
> 	if(ssum+si[p]>=0&&fsum+fi[p]>=0)//左子树
> 		dfs(p+1,ssum+si[p],fsum+fi[p],sum+sumn[p]);
> 	  dfs(p+1,ssum,fsum,sum);//右子树
> }
> int main()
> {
> 	int i;
> 	cin>>n;
> 	for(i=1;i<=n;i++)
> 	{
> 		cin>>si[i]>>fi[i];
> 		sumn[i]=si[i]+fi[i];
> 	}
> 	dfs(1,0,0,0);
> 	cout<<ans<<endl;
> 	return 0;
> 
> }