#include<stdio.h>
#include<algorithm>
#define MAXN 100000
struct interval
{
    int st,dr;
};
bool cmp(interval,interval);
int cautbin(int i);
FILE*fin,*fout;
interval v[MAXN+1];
int d[MAXN+1];
int main()
{
    fin=fopen("heavymetal.in","r");
    fout=fopen("heavymetal.out","w");
    int N;
    fscanf(fin,"%d",&N);
    for(int i=1;i<=N;i++)
    {
        fscanf(fin,"%d%d",&v[i].st,&v[i].dr);
    }
    std::sort(&v[1],&v[N+1],cmp);
    d[1]=v[1].dr-v[1].st;
    for(int i=2;i<=N;i++)
    {
        int j=cautbin(i);
        d[i]=std::max(d[i-1],d[j]+v[i].dr-v[i].st);
    }
    fprintf(fout,"%d",d[N]);
    fclose(fin);
    fclose(fout);
    return 0;
}
bool cmp(interval a,interval b)
{
    return a.dr<b.dr;
}
int cautbin(int i)
{
    int st=1,dr=i-1;
    while(st<=dr)
    {
        int mij=(st+dr)>>1;
        if(v[mij].dr>v[i].st)
        {
            dr=mij-1;
        }
        else
        {
            st=mij+1;
        }
    }
    return st-1;
}