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