#include <fstream>
#include <algorithm>
#define X first
#define Y second
using namespace std;
int n, x, y, i, j, sol, st, dr;
pair <int, int> A[100001];

int main () {
      ifstream fin ("heavymetal.in");
      ofstream fout ("heavymetal.out");
      fin>>n;
      sol=0;
      for (i=1;i<=n;i++) {
            fin>>A[i].X>>A[i].Y;
      }

      sort(A+1, A+n+1);
/**
      for (i=1;i<=n;i++)
            fout<<A[i].X<<" "<<A[i].Y<<"\n";
*/
      st=A[1].X;
      dr=A[1].Y;
      for (i=2;i<=n;i++) {
            if (A[i].X<=dr) {
                  if (A[i].Y>dr)
                        dr=A[i].Y;
            } else {
                  sol+=dr-st;
                  st=A[i].X;
                  dr=A[i].Y;
            }
      }

      sol+=dr-st;
      fout<<sol;

      return 0;
}