#include<bits/stdc++.h>
using namespace std;
int main()
{
    long long maxx=0,k,n,a1,b1,a2,b2;
	cin>>n>>a1>>b1;
	maxx=a1+b1;
	for(long long i=2;i<=n;i++)
	{
		cin>>a2>>b2;
		if(maxx<a2)
		{
			k+=a2-maxx;
			maxx=a2+b2+k;
		}
		else
		{
			maxx=max(maxx,a2+b2+k);
		}
	}
	cout<<k<<endl;
	return 0;
}

50分，#1#7#8#9#10WA，测试点信息：https://www.luogu.com.cn/record/177322805