#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("heavymetal.in");
ofstream cout("heavymetal.out");
const int nmax=100000;
struct fint
{
    int st,dr;
};
int n;
fint v[nmax+5];
int dp[nmax+5];
bool cmp(fint a,fint b)
{
    if(a.dr==b.dr)
        return a.st<b.st;
    return a.dr<b.dr;
}
int main()
{
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>v[i].st>>v[i].dr;
    sort(v+1,v+n+1,cmp);
    for(int i=1;i<=n;i++)
    {
        int lm=0;
        for(int j=1;j<i;j++)
        {
            if(v[j].dr<=v[i].st)
                lm=max(lm,dp[j]);
        }
        dp[i]=lm+v[i].dr-v[i].st;
    }
    cout<<dp[n];
    return 0;
}