#include<cstdio>
#include<algorithm>
#include<cstring>
#define Nmax 100005
#define Inf 1000000000
using namespace std;
int n,i,j,p,q,nr;
int sol;
int w[Nmax],a[Nmax];
struct nod
{
    int x;
    int y;
}v[Nmax];
int cmp(const nod a,const nod b)
{
    if (a.y==b.y) return a.x<b.x;
    return a.y<b.y;
}
int cb(int val)
{
    int st=1,dr=i-1,m,Max=0;
    while (st<=dr)
    {
        m=(st+dr)/2;
        if (v[m].y<=val) Max=max(Max,v[m].y);
        if (v[m].y<=val && v[m+1].y>val) return m;
        if (v[m].y<=val) st=m+1;
        else dr=m-1;
    }
    return Max;
}
int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    scanf("%d",&n);
    for (i=1;i<=n;i++)
    scanf("%d %d",&v[i].x,&v[i].y);
    sort(v+1,v+n+1,cmp);
    for (i=1;i<=n;i++)
    {
        a[i]=a[i-1];
        p=cb(v[i].x);
        a[i]=max(a[i],a[p]+v[i].y-v[i].x);
        if (a[i]>sol) sol=a[i];
    }
    printf("%d",sol);
    return 0;
}