#include<iostream>
#include<algorithm>
#include<cmath>
#include<vector>
#include<stack>
#include<queue>
#include<set>
#include<map>
#define x first
#define y second
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
using namespace std;
// #define int long long
signed main(){
  int n;
  cin >> n;
  int l,r;
  vector<pair<int,int> >v;
  while(n--){
    cin >> l >> r;
    v.pb(mp(l,1));
    v.pb(mp(r,-1));
  }
  sort(all(v));
  int bal = 0,ans = 0,prev = v[0].x;
  for(int i = 0;i < v.size();i++){
    if(bal){
      ans+=(v[i].x - prev);
    }
    prev = v[i].x;
    bal+=v[i].y;
  }
  cout << ans;
  return 0;
}