#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;
typedef pair<int,int> PII;
const int N = 2010;
struct node{
    int l,r;
}t1[N],t2[N];
int n;

bool cmp(node &a,node &b){
    if(a.l != b.l) return a.l < b.l;
    return a.r < b.r;
}

int main(){
    cin >> n;
    for(int i = 0;i < 2 * n;i++) cin >> t1[i].l >> t1[i].r;

    sort(t1,t1 + 2 * n,cmp);
    vector<PII> res;
    int st = -2e9,ed = st;
    for(int i = 0;i < 2 * n;i++){
        int tl = t1[i].l,tr = t1[i].r;
        if(tl > ed){
            st = tl,ed = tr;
        }else{
            if(tr <= ed){
                res.push_back({tl,tr});
                st = tl;
            }else{
                res.push_back({tl,ed});
                st = ed,ed = tr;
            }
        }
    }
    int cnt = 0;
    for(auto t : res)
        cnt += t.second - t.first;
    cout << cnt << endl;

    return 0;
}