#include <fstream>
#include <algorithm>
using namespace std;
const int nmax=100005;
ifstream fin ("heavymetal.in");
ofstream fout ("heavymetal.out");
struct interval
{
    int x,y;
}v[nmax];
bool cmp(interval a,interval b)
{
    return a.y<b.y;
}
int main()
{
    int n,dp[nmax],rez=0;
    fin >> n;
    for (int i=1;i<=n;i++)
    {
        fin >> v[i].x >> v[i].y;
    }
    sort (v+1,v+n+1,cmp);
    dp[n]=v[n].y-v[n].x;
    for (int i=n-1;i>=1;i--)
    {
        dp[i]=v[i].y-v[i].x;
        for (int j=i+1;j<=n;j++)
        {
            if (v[j].x>=v[i].y) dp[i]=max(dp[j]+v[i].y-v[i].x,dp[i]);
        }
    }
    for (int i=1;i<=n;i++)
    {
        rez=max(dp[i],rez);
    }
    fout << rez;
}