#include<fstream>
#include<algorithm>
using namespace std;
ifstream cin("heavymetal.in");
ofstream cout("heavymetal.out");
struct dot{int X;int Y;};int cmp(dot x,dot y){if(x.X!=y.X)return x.X<y.X;else return x.Y<y.Y;}dot v[100003];
int n,i,a[100003],st,dr,mij;
int main()
{
    cin>>n;
    for(i=1;i<=n;i++)
       cin>>v[i].X>>v[i].Y;
    sort(v+1,v+n+1,cmp);
    a[1]=v[1].X-v[1].Y;
    for(i=2;i<=n;i++)
    {
        st=i;dr=i-1;
        a[i]=a[i-1];
        while(st<=dr)
        {
            mij=st+(dr-st)/2;
            if(v[i].X>=v[mij].Y)
            st=mij+1;
            else
            dr=mij-1;
        }
        if(a[i]<=a[st]+v[i].Y-v[i].X)
        a[i]=a[st]+v[i].Y-v[i].X;
    }
    cout<<a[n];
}