#include<cstdio>
#include<algorithm>
using namespace std;
struct trupe
{
    int x,y;
};
trupe v[100005];
int a[100005];
int bs(int st,int dr,int nr)
{
    int mid,ult=-1;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        if(v[mid].y<=nr)
        {
            ult=mid;
            st=mid+1;
        }
        else
            dr=mid-1;
    }
    return ult;
}
bool cmp(trupe a,trupe b)
{
    return a.y<b.y;
}
int main()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    int n,i,j,max1=-1;
    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++)
    {
        j=bs(1,n,v[i].x);
        a[i]=max(a[i-1],a[j]+v[i].y-v[i].x);
        if(a[i]>max1) max1=a[i];
    }
    printf("%d",max1);
    return 0;
}