#include <fstream>
#include <algorithm>
using namespace std;

ifstream cin ("heavymetal.in");
ofstream cout ("heavymetal.out");

const int MAX = 100002;

struct sp{
    int dr, st;
}v[MAX];

int n, dp[MAX];

bool cmp(sp a, sp 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;
        int 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[i]<v[i].dr-v[i].st+dp[dr])
            dp[i] = v[i].dr-v[i].st+dp[dr];
    }
    cout << dp[n];
    return 0;
}