#include<cstdio>
#include<fstream>
#include<iostream>
#include<iomanip>
#include<algorithm>
#include<vector>
#include<bitset>
#include<deque>
#include<queue>
#include<set>
#include<map>
#include<cmath>
#include<cstring>
#include<ctime>
#include<cstdlib>
#include<unordered_map>

#define ll long long
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
#define pll pair<ll,ll>

using namespace std;

const int nmax = 100005;

int n, l, r, m, i, j;
ll dp[nmax], sol;

struct interval
{
    int x, y;
};
interval p[nmax];

struct cmp
{
    bool operator () (interval a, interval b) const
    {
        return a.y < b.y;
    }
};

int main()
{
    freopen("heavymetal.in", "r", stdin);
    freopen("heavymetal.out", "w", stdout);

    scanf("%d", &n);

    for(i = 1; i <= n; i++)
        scanf("%d%d", &p[i].x, &p[i].y);

    sort(p + 1, p + n + 1, cmp());

    dp[1] = p[1].y - p[1].x;
    sol = dp[1];

    for(i = 2; i <= n; i++)
    {
        dp[i] = dp[i - 1];

        l = 1;
        r = i - 1;
        while(l <= r)
        {
            m = (l + r) / 2;
            if(p[m].y <= p[i].x)
            {
                j = m;
                l = m + 1;
            }
            else
                r = m - 1;
        }

        dp[i] = max(dp[i], dp[j] + p[i].y - p[i].x);

        sol = max(sol, dp[i]);
    }

    printf("%lld\n", sol);

    return 0;
}