#include <bits/stdc++.h>
using namespace std;

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

struct concert
{
    int x,y,z;
};

bool Comp(concert a, concert b)
{
    return a.y < b.y;
}

concert a[100003];
int n, dp[100003];

int CautBin(int x, int dr)
{
    int st = 1, mij, p = 0;
    while (st <= dr)
    {
        mij = (st + dr) / 2;
        if (x < a[mij].y) dr = mij - 1;
        else
        {
            p = mij;
            st = mij + 1;
        }
    }
    return p;
}

int main()
{
    int i, j;
    fin >> n;
    for (i = 1; i <= n; i++)
    {
        fin >> a[i].x >> a[i].y;
        a[i].z = a[i].y - a[i].x;
    }
    sort(a + 1, a + n + 1, Comp);
    dp[1] = a[1].z;
    for (i = 2; i <= n; i++)
    {
        j = CautBin(a[i].x, i - 1);
        dp[i] = max(dp[i - 1], dp[j] + a[i].z);
    }
    fout << dp[n] << "\n";
    return 0;
}