#include<bits/stdc++.h>
using namespace std;
#define int long long
struct segtree {
int n;
vector<int> sum, pre;
segtree(vector<int>& a) {
n=a.size();
while (n&(n-1)) n++;
sum.assign(2*n, 0); pre.assign(2*n, 0);
for (int i = n; i < n+a.size(); ++i) pre[i]=sum[i]=a[i-n];
for (int i = n-1; i > 0; --i) {
sum[i]=sum[2*i]+sum[2*i+1];
pre[i]=max(pre[2*i], sum[2*i]+pre[2*i+1]);
}
}
pair<int, int> query(int ql, int qr, int v=1, int nl=1, int nr=-1) {
if (v==1) nr=n;
if (ql>nr || qr<nl) return {0, 0};
if (ql<=nl && nr<=qr) return {sum[v], pre[v]};
auto [s1, p1] = query(ql, qr, 2*v, nl, (nl+nr)/2);
auto [s2, p2] = query(ql, qr, 2*v+1, (nl+nr)/2+1, nr);
return {s1+s2, max(p1, s1+p2)};
}
void update(int u, int v) {
u+=n-1;
sum[u]=pre[u]=v;
for (u/=2; u>0; u/=2) {
sum[u]=sum[2*u]+sum[2*u+1];
pre[u]=max(pre[2*u], sum[2*u]+pre[2*u+1]);
}
}
};
vector<int> a, b, p;
bool acomp(int x, int y) { return a[x]<a[y]; }
signed main() {
cin.tie(0)->sync_with_stdio(false);
int n, m=0;
cin >> n;
a.assign(n, 1);
b.assign(n, 1);
p.assign(n, 1);
for (int i = 0; i < n; ++i) {
cin >> a[i] >> b[i];
m=max(m, b[i]);
p[i]=i;
} sort(p.begin(), p.end(), acomp);
vector<int> c(n); c[0]=a[0];
for (int i = 1; i < n; ++i) {
c[i]=b[p[i]]-a[p[i]]+a[p[i-1]];
} segtree st(c);
for (int i = 0; i < n-1; ++i) {
m=max(m, b[p[i]]+st.query(i+2, n).second);
} cout << m << '\n';
return 0;
}
