#pragma GCC optimize("fast-math")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
using namespace std;
ll n, maxi, dp[100005];
struct muz
{
    ll st, dr;
    bool operator <(const muz & ob)const
    {
            return dr < ob.dr;
    }
}v[100005];

ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int32_t main(int argc, char * argv[])
{
    fin >> n;
    for(int i = 1; i <= n; ++i)
    {
        fin >> v[i].st >> v[i].dr; // pt fiecare interval presupun ca incep muzica de la el si caut urmatorul element mai mare ca el si tot asa cu suma maxima
    }
    sort(v + 1, v + n + 1);
    /*for(int i = 1; i <= n; ++i)
    {
        fout << v[i].st << " " << v[i].dr << '\n';
    }
    **/
    dp[1] = v[1].dr - v[1].st;
    for(int i = 2; i <= n; ++i)
    {
        ll interval = v[i].dr - v[i].st;
        ll st = 1, dr = i - 1, mid = 0, sol = 0; // cap drept al sol sa fie mai mic sau egal cu cap stang al v[i] si sa aiba dp maxim
        while(st <= dr)
        {
            mid = (st + dr) / 2;
            if(v[mid].dr <= v[i].st)
            {
                sol = mid;
                st = mid + 1;
            }
            else
            {
                dr = mid - 1;
            }
        }
        dp[i] = max(dp[i - 1], dp[sol] + interval);
    }
    fout << dp[n];
    return 0;
}