#include<cstdio>
#include<algorithm>
using namespace std;
struct interval
{
    int st,dr;
};
interval a,b,v[100010];
int bs;
int n,i,j,rez,best[100010],temp,tmax;
bool cmp(const interval &a,const interval &b)
{
    return a.dr<b.dr;
}
int bins(int st,int dr)
{
    int last,med;
    while(st<=dr)
    {
        med=((dr-st)>>1)+st;
        if(v[med].dr<=v[i].st)
        {
            st=med+1;
            last=med;
        }
        else
        {
            dr=med-1;
        }
    }
    return last;
}
int main()
{
    int st,dr;
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d%d",&st,&dr);
        a.st=st;
        a.dr=dr;
        v[i]=a;
    }
    sort(v+1,v+n+1,cmp);
    for(i=1;i<=n;i++)
    {
        best[i]=best[i-1];
        temp=bins(1,i);
        if(best[temp]+(v[i].dr-v[i].st)>best[i])
            best[i]=best[temp]+(v[i].dr-v[i].st);
    }
    printf("%d\n",best[n]);
    return 0;
}