#include <iostream>
#include <cstdio>
#include <algorithm>
#define MAXN 100050

using namespace std;

struct concert
{
    int a, b;
    bool operator()(concert e, concert f)
    {
        return e.b < f.b;
    }
};
int n, din[MAXN];
concert c[MAXN];

void solve()
{
    for (int i = 1; i <= n; i++)
    {
        din[i] = din[i-1];
        int step, val;
        for (step = 1; step <= i; step <<= 1);
        for (val = 0; step; step >>= 1) {
            if (val + step <= i && c[val+step].b <= c[i].a)
                val += step;
        }
        din[i] = max(din[i], din[val] + (c[i].b - c[i].a));
    }
}

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

    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
        scanf("%d %d", &c[i].a, &c[i].b);
    sort(c+1, c+n+1, concert());
    solve();
    printf("%d", din[n]);

    return 0;
}