#include <bits/stdc++.h>
#define NMAX 100005
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
int n;
vector < pair <int,int> > v;
long long dp[NMAX],maxim;
int main()
{
    f>>n;
    v.push_back({0,0});
    for(int i=1;i<=n;i++)
    {
        int x,y;
        f>>x>>y;
        v.push_back({y,x});
    }
    sort(v.begin(),v.end());
    for(int i=1;i<=n;i++)
    {
        int st=0;
        int dr=i-1;
        int sol=0;
        while(st<=dr)
        {
            int mid=(st+dr)/2;
            if(v[mid].first<=v[i].second)
            {
                sol=mid;
                st=mid+1;
            }
            else
                dr=mid-1;
        }
        dp[i]=max(dp[i-1],v[i].first-v[i].second+dp[sol]);
        maxim=max(dp[i],maxim);
    }
    g<<maxim;
    return 0;
}