#include <bits/stdc++.h>
using namespace std;
#define int long long
const int INF=1e18;
int n;
vector<pair<int,int>>aw;
signed main()
{
cin>>n;
aw.resize(n);
for(int i=0;i<n;i++) cin>>aw[i].first>>aw[i].second;
sort(aw.begin(),aw.end());
vector<int>p(n);
p[0]=aw[0].second;
for(int i=1;i<n;i++) p[i]=p[i-1]+aw[i].second;
vector<int>smx(n,-INF);
smx[n-1]=p[n-1]-aw[n-1].first;
for(int i=n-2;i>=0;i--) smx[i]=max(smx[i+1],p[i]-aw[i].first);
int res=-INF;
for(int i=0;i<n;i++){
int mns=((!i)?0:p[i-1]);
int ii=aw[i].first-mns;
int jj=smx[i];
res=max(res,ii+jj);
}
cout<<res<<endl;
}
