#include <bits/stdc++.h>

using namespace std;

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

const int N = 1000005;

pair < int, int > a[N];

int dp[N];

void usain_bolt()
{
    ios::sync_with_stdio(false);
    fin.tie(0);
}

int bs(int k, int n)
{
    int sol = 0;
    int st = 1, dr = n;
    while(st <= dr) {
        int mid = (st + dr) >> 1;
        if(k > a[mid].second) {
                sol = max(sol, mid);
                st = mid + 1;
        }
        else dr = mid - 1;
    }
    return sol;
}

int main()
{
    usain_bolt();

    int n;

    fin >> n;
    for(int i = 1; i <= n; ++i)
        fin >> a[i].first >> a[i].second;

    sort(a + 1, a + 1 + n);

    int ans = 0;

    for(int i = 1; i <= n; ++i) {
        int pos = bs(a[i].first, i);
        dp[i] = max(dp[i - 1], dp[pos] + a[i].second - a[i].first);
    }

    for(int i = 1; i <= n; ++i) ans = max(ans, dp[i]);

    fout << ans;

    return 0;
}