#include <fstream>
#include <algorithm>
#define DIM 100005

using namespace std;

ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
int N,best[DIM];
pair <int,int> v[DIM];
int cautbin(int x,int lim){
    int p,u,mid,sol=0;
    p=1;
    u=lim;
    while(p<=u){

        mid=(p+u)>>1;
        if(v[mid].second<=x){
            p=mid+1;
            sol=mid;
        }
        else
            u=mid-1;
    }
    return sol;

}
int main(){
    fin>>N;
    for(int i=1;i<=N;i++)
        fin>>v[i].first>>v[i].second;
    sort(v+1,v+N+1);
    best[1]=v[1].second-v[1].first;
    for(int i=2;i<=N;i++){
        best[i]=max(best[i-1],v[i].second-v[i].first);
        int x=cautbin(v[i].first,i-1);
        best[i]=max(best[i],best[x]+v[i].second-v[i].first);
    }
    fout<<best[N];
    fin.close();fout.close();
    return 0;
}