#include <fstream>
#include <algorithm>
# define NMAX 100005
using namespace std;

ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
int n,d[NMAX],sol;

struct metal
{
   int st,dr;
} v[NMAX];

void citire()
{
    int i;
    f>>n;
    for (i=1; i<=n; i++)
        f>>v[i].st>>v[i].dr;
}

int comp(metal a,metal b)
{
    return (a.dr < b.dr || a.dr == b.dr && a.st < b.st);
}

int caut(int x)
{
    int m, p = 1, u = n;
    while (p<=u)
    {
        m = (p+u)/2;
        if (x >= v[m].dr) p = m+1;
        else u = m-1;
    }
    return u;
}

void solve()
{
    int i,j,k;
    for (i=1; i<=n; i++)
    {
        j = caut(v[i].st);
        d[i] = max(d[i-1], d[j] + v[i].dr - v[i].st);
        sol = max(sol, d[i]);
    }
    g<<sol;
}

int main()
{
    citire();
    sort(v+1,v+1+n,comp);
    solve();
    return 0;
}