#include <bits/stdc++.h>
#define IOS ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define int long long
using namespace std;
///Constants
//int mod = 1000000007;
/*void setIO(string s)
{
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}*/
signed main()
{
IOS;
int n, a, b, temp = 0;
cin >> n;
vector<pair<int, int>>v;
v.push_back({0, 0});
for(int i = 0 ; i < n ; ++i){
cin >> a >> b;
v.push_back({a, b});
}
sort(v.begin(), v.end());
a = 0;
for(int i = 0 ; i <= n ; ++i){
a+=v[i].second;
v[i].second = a;
if(v[i].first>v[i].second){
v[i].first = -1;
v[i].second = -1;
temp++;
}
}
sort(v.begin(), v.end());
int mx = -1;
for(int i = temp ; i < n ; ++i){
for(int j = i+1 ; j <= n ; ++j){
mx = max(mx, (v[j].second-v[i].second)-(v[j].first-v[i+1].first));
// cout << i << " " << j << " " << mx << "\n";
}
}
cout << mx ;
return 0;
}
