#include <bits/stdc++.h>
#define f0(i, n) for(int i(0); i < (n); i++)
#define f1(i, n) for(int i(1); i <= n; i++)
using namespace std;
typedef long long ll;
const int N = 500002;
struct data{
ll a, b;
} a[N];
bool cmp(data a1, data a2){
return a1.a < a2.a;
}
int n; ll f[N];
int main(){
ios_base::sync_with_stdio(0);
cin >> n;
f1(i, n) cin >> a[i].a >> a[i].b;
sort(a + 1, a + n + 1, cmp);
ll ma = 0;
f1(i, n){
f[i] = a[i].b;
f[i] = max(f[i], ma + a[i].b - a[i].a);
ma = max(ma, f[i] + a[i].a);
}
cout << *max_element(f + 1, f + n + 1);
}
