#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("cool.in");
ofstream cout("cool.out");
const int MAX=100001;
struct interval{
    int st, dr;
} v[MAX];
int n;
bool cmp(interval a, interval b) {
    return a.dr<b.dr;
}
int main ()
{
    cin>>n;
    for(int i=1; i<=n; ++i){
        cin>>v[i].st>>v[i].dr;
    }
    sort(v+1, v+n+1, cmp);
    for(int i=1; i<=n; ++i) {
        dp[i]=dp[i-1];
        int st=1, dr=i-1;
        while(st<=dr){
            int mij=(st+dr)/2;
            if(v[mij].dr<=v[i].st){
                st=mij+1;
            } else{
                dr=mij-1;
            }
        }
        if(dp[dr]+v[i].dr-v[i].st>dp[i]) {
            dp[i]=dp[dr]+v[i].dr-v[i].st;
        }
    }
    cout<<dp[n];


    return 0;
}