#include <cstdio>
#include <algorithm>
using namespace std;
const int NMAX=100000;
struct interval{
    int x,y;
};
interval s[NMAX+5];
int d[NMAX+5];
bool cmp(const interval &a, const interval &b)
{
    return a.y<b.y;
}
int max(int a, int b, int c)
{
    int max=a;
    if(max<b)
        max=b;
    if(max<c)
        max=c;
    return max;
}
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;
    register int i;
    scanf("%d",&n);
    int a,b,j;
    for(i=1;i<=n;++i)
    {
        scanf("%d%d",&a,&b);
        s[i].x=a;s[i].y=b;
    }
    sort(s+1,s+n+1,cmp);
    //d[1]=s[1].y-s[1].x;
    for(i=1;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;
}