#include<iostream>
#include<algorithm>
using namespace std;
int N;
int A[2<<17];
long ans,now;
main()
{
	cin>>N;
	for(int i=0;i<2*N;i++)
	{
		cin>>A[i];
		if(i%2==0)now-=A[i];
		else now+=A[i];
	}
	ans=now;
	for(int i=0;i<N;i++)
	{
		now+=2*A[2*i]-2*A[2*i+1];
		ans=max(ans,now);
	}
	cout<<ans<<endl;
}