#include <bits/stdc++.h>
using namespace std;
ifstream in("heavymetal.in");
ofstream out("heavymetal.out");
int n,dp[100005],j;
struct timp
{
    int r,l;
}v[100005];
bool comp(timp x, timp y)
{
    return (x.l<y.l or (x.l==y.l and x.r<y.r));
}
int main()
{
    in>>n;
    for(int i=1;i<=n;i++)
    {
        in>>v[i].r>>v[i].l;
    }
    sort(v+1,v+n+1,comp);
    dp[1]=v[1].l-v[1].r;
    for(int i=2;i<=n;i++)
    {
        int st,dr;
        st=1;dr=i-1;
        while(st<=dr)
        {
            int mij=(st+dr)/2;
            if(v[mij].l<=v[i].r)
            {
                j=mij;st=mij+1;
            }
            else dr=mij-1;
        }
      dp[i]=max(dp[i-1],dp[j]+v[i].l-v[i].r);
    }
    out<<dp[n];
}