#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin ("heavymetal.in");
ofstream fout ("heavymetal.out");
int n,i,a,b,maxi,s[100001],st,dr,mid,j;
struct duten_pula_mea_de_ghinda {int start,finish,length;}v[100001];

int compare (duten_pula_mea_de_ghinda a, duten_pula_mea_de_ghinda b)
{
    return a.finish<b.finish||a.finish==b.finish&&a.start>=b.start;
}
int cautbin (int x)
{
    int st=1,dr=n;
    while (st<=dr)
    {
        mid=(st+dr)/2;
        if (v[mid].finish>x) dr=mid-1;
        else st=mid+1;
    }
    mid=(st+dr)/2;
   // fout<<v[st].finish<<" "<<v[mid].finish<<" "<<v[dr].finish<<" "<<x<<endl;
    if (v[st-1].finish==x) return st-1;

    else return -1;


}
int main()
{
    fin>>n;
    for (i=1;i<=n;i++)
    {
        fin>>v[i].start>>v[i].finish;
        v[i].length=v[i].finish-v[i].start;
    }
    sort (v+1,v+n+1,compare);
    for (j=1;j<=v[n].finish;j++)
    {
       int t=cautbin(j); //fout<<j<<" "<<t<<endl;
        if (t==-1) s[j]=s[j-1];

        else
        {
            s[j]=max(s[j],s[v[t].start]+v[t].length);
        }
        if (s[j]>maxi) maxi=s[j];
    }
    fout<<maxi;
    return 0;
}