#include <bits/stdc++.h>
#define endl "\n"
#define ll long long
using namespace std;

ifstream fin ("heavymetal.in");
ofstream fout("heavymetal.out");

#define cin  fin
#define cout fout

bool cmp(pair < int , int > a, pair < int , int > b) {
    return a.second <= b.second;
}

void cb(vector < pair < int, int > >a, int left, int right, int index, int &sol) {
    while(left <= right) {
        int mid = (left + right) / 2;
        if(a[mid].second > a[index].first) {
            right = mid - 1;
        } else {
            left  = mid + 1;
            sol   = mid;
        }
    }
}

void solve() {
    int n;
    cin >> n;
    vector < pair < int , int > > a(n + 1);
    vector < int > dp(n + 1);
    for(int i=1; i <= n; i++) {
        cin >> a[i].first >> a[i].second;
    }
    /*
    for(auto &it: a) {
        cin >> it.first >> it.second;
    }
    */
    sort(a.begin() + 1, a.end(), cmp);
    for(int i=1; i <= n; i++) {
        int sol = 0;
        cb(a, 0, i - 1, i, sol);
        dp[i] = max(dp[i-1] , dp[sol] + a[i].second - a[i].first);
    }
    cout << dp[n];

}

int main() {
    ios_base::sync_with_stdio(0);
    cin .tie(0);
    cout.tie(0);

    int testCases = 1;
    //cin >> testCases;
    while(testCases--) {
        solve();
    }
}