#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;
ifstream fin("heavymetal.in");
ofstream fout("heavymetal.out");
vector <pair<int, int>>v;
int main()
{
  long long n, i, start, final, var, total=0;
  fin>>n;
  for(i=1; i<=n; i++)
  {
    fin>>start>>final;
    v.push_back(make_pair(final, start));
  }
  
  sort(v.begin(), v.end());
  
  var=v[0].first;
  
  for(i=1; i<n; i++)
  {
    if(var<=v[i].second)
    {
      total += abs(v[i].first - var);
      var=v[i].first;
    }
  }
    
    fout<<total;
    return 0;
    
}