#include <fstream>
#include <algorithm>
#define DIM 100001

using namespace std;

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

int N;
long long best[DIM], maxc;  // durata maxima ce se poate obtine pana la spectacolul i
struct show
{
   int start, end;
}s[DIM];

bool comp(const show &unu, const show &doi)
{
    if( unu.start == doi.start )
    {
        return unu.end < doi.end;
    }
    return unu.start < doi.start;
}

int main()
{
    int i, j;

    in >> N;
    for(i = 1; i <= N; i++)
    {
        in >> s[i].start >> s[i].end;
    }
    sort(s+1, s+N+1, comp);
    best[1] = s[1].end - s[1].start;
    for (i = 2; i <= N; i++)
    {
        maxc = 0;
        for (j = i-1; j >= 1; j--)
        {
            if( s[i].start >= s[j].end && best[j] > maxc )
            {
                maxc = best[j];
            }
        }
        best[i] = s[i].end - s[i].start;
        best[i] = best[i] + maxc;
    }
    maxc = 0;
    for(i = 1; i <= N; i++)
    {
        if( best[i] > maxc )
        {
            maxc = best[i];
        }
    }
    out << maxc;
    return 0;
}