#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF = 1e18+7;
const ll MOD = 998244353;
typedef pair<ll,ll> ii;
#define iii pair<ii,ll>
#define f(i,a,b) for(ll i = a;i < b;i++)
#define pb push_back
#define vll vector<ll>
#define F first
#define S second
#define all(x) (x).begin(), (x).end()
///I hope I will get uprating and don't make mistakes
///I will never stop programming
///sqrt(-1) Love C++
///Please don't hack me
///@TheofanisOrfanou Theo830
///Think different approaches (bs,dp,greedy,graphs,shortest paths,mst)
///Stay Calm
///Look for special cases
///Beware of overflow and array bounds
///Think the problem backwards
///Training
int main(void){
ios_base::sync_with_stdio(0);
cin.tie(0);
ll ans = 0;
ll n;
cin>>n;
vector<ii>arr;
f(i,0,n){
ll a,b;
cin>>a>>b;
arr.pb(ii(a,b));
}
sort(all(arr));
vll ar;
ll last = 0;
ll pre[n+1] = {0};
f(i,0,n){
ar.pb(arr[i].S - arr[i].F + last);
last = arr[i].F;
pre[i+1] = pre[i] + ar.back();
}
ll suf[n];
suf[n-1] = pre[n];
for(ll i = n-2;i >= 0;i--){
suf[i] = max(suf[i+1],pre[i+1]);
}
last = 0;
f(i,0,n){
ans = max(ans,suf[i] - pre[i] + arr[i].F - last);
last = arr[i].F;
}
cout<<ans<<"\n";
}
