#include<fstream>
#include<algorithm>
using namespace std;
ifstream cin("heavymetal.in");
ofstream cout("heavymetal.out");
struct dot{int u;int p;};int cmp(dot x,dot y){if(x.u!=y.p) return x.u<y.u;else return x.p<y.p;}dot v[100003];
int n,i,a[100003],st,dr,mij;
int main()
{
    cin>>n;
    for(i=1;i<=n;i++)
       cin>>v[i].p>>v[i].u;
    sort(v+1,v+n+1,cmp);
    a[1]=v[1].u-v[1].p;
    for(i=2;i<=n;i++)
    {
        st=1;dr=i-1;
        a[i]=a[i-1];
        while(st<=dr)
        {
            mij=st+(dr-st)/2;
            if(v[i].p>=v[mij].u)
            st=mij+1;
            else
            dr=mij-1;
        }
        if(a[i]<a[dr]+v[i].u-v[i].p)
           a[i]=a[dr]+v[i].u-v[i].p;
    }
    cout<<a[n];
    return 0;
}