#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
void solve() {
int N;
cin >> N;
pair<ll, ll> A[N+1];
A[0].first = A[0].second = 0;
for (int i = 1; i <= N; i++)
cin >> A[i].first >> A[i].second;
sort(A+1, A+N+1);
ll CUM[N+1];
CUM[0] = 0;
for (int i = 1; i <= N; i++)
CUM[i] = CUM[i-1] + A[i].second;
priority_queue<pair<ll, int>> pq;
ll S = 0;
for (int i = 1; i <= N; i++) {
S += A[i].second - A[i].first + A[i-1].first;
pq.push({S, i});
}
ll ans = 0;
for (int i = 1; i <= N; i++) {
while(pq.top().second < i) pq.pop();
if (pq.size()) ans = max(ans, CUM[pq.top().second] - CUM[i-1] + A[i].first - A[pq.top().second].first);
}
cout << ans;
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
solve();
}
