#include <bits/stdc++.h>

using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int n, dp[200003]; ///dp[i] = durata max daca termin la o poz <= i
vector<int> aux;

struct Iris {
    int st, dr, lung;
}v[100003];

inline int cmp(Iris &a, Iris &b) { return a.dr < b.dr; }

int main()
{
    fin >> n;
    for(int i=1; i<=n; i++) {
        fin >> v[i].st >> v[i].dr;
        v[i].lung = v[i].dr - v[i].st;
        aux.push_back(v[i].st);
        aux.push_back(v[i].dr);
    }
    sort(aux.begin(), aux.end());
    vector<int>::iterator it = unique(aux.begin(), aux.end());
    aux.resize(distance(aux.begin(), it));
    for(int i=1; i<=n; i++) {
        v[i].st = lower_bound(aux.begin(), aux.end(), v[i].st) - aux.begin() + 1;
        v[i].dr = lower_bound(aux.begin(), aux.end(), v[i].dr) - aux.begin() + 1;
    }
    sort(v+1, v+n+1, cmp);
    int idx = 1;
    for(int i=1; i<=v[n].dr; i++) {
        dp[i] = dp[i - 1];
        while(v[idx].dr == i) dp[i] = max(dp[i], dp[v[idx].st] + v[idx].lung), idx++;
    }
    fout << dp[v[n].dr];

    return 0;
}