#include <cstdio>
#include <algorithm>
using namespace std;
const int NMAX=100000;
int d[NMAX+5];
struct interval
{
    int x,y;
};
interval s[NMAX+5];
bool cmp(const interval &a,const interval &b)
{
    return a.y<b.y;
}
int bs(int st,int dr,int val)
{
    int med,last=-1;
    while (st<=dr)
    {
        med=(st+dr)>>1;
        if (s[med].y<=val)
        {
            last=med;
            st=med+1;
        }
        else
            dr=med-1;
    }
    return last;
}
int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    int n,j,x,y;
    scanf("%d",&n);
    for (register int i=1;i<=n;++i)
    {
        scanf("%d%d",&x,&y);
        s[i].x=x;
        s[i].y=y;
    }
    sort(s+1,s+n+1,cmp);
    d[1]=s[1].y-s[1].x;
    for (register int i=2;i<=n;++i)
    {
        d[i]=d[i-1];
        j=bs(1,i-1,s[i].x);
        if (j==-1)
        {
            if (d[i]<s[i].y-s[i].x)
                d[i]=s[i].y-s[i].x;
        }
        else
            if (d[i]<d[j]+s[i].y-s[i].x)
                d[i]=d[j]+s[i].y-s[i].x;
    }
    printf("%d\n",d[n]);
    return 0;
}