#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");

long long n, i, d[100010], st, dr, stangaCrt, dreaptaMij, mij, maxim, intervalCrt;
pair <long long, long long> v[100010];

int main(){
    fin>>n;
    for(i=1; i<=n; i++){
        fin>>v[i].second>>v[i].first;
    }
    sort(v+1, v+n+1);
    d[1]=v[1].first-v[1].second;
    for(i=2; i<=n; i++){
        st=1;
        dr=i-1;
        stangaCrt=v[i].second;
        intervalCrt=v[i].first-stangaCrt;
        while(st<=dr){
            mij=(st+dr)/2;
            dreaptaMij=v[mij].first;
            if(dreaptaMij>stangaCrt){
                dr=mij-1;
            }else{
                st=mij+1;
            }
        }
        d[i]=max(d[i-1], d[dr]+intervalCrt);
        maxim=max(maxim, d[i]);
    }
    fout<<maxim;
}