#include <stdio.h>   
  
#include <vector>   
#include <algorithm>   
  
using namespace std;   
  
vector<pair<int, int> > v;   
int i,j,a,b,n,lungime,x;   
  
int main()   
{   
freopen("heavymetal.in","rt",stdin);   
freopen("heavymetal.out","wt",stdout);   
     scanf("%d", &n);   
      v.clear();   
      for (i=0;i<n;i++)   
      {   
      scanf("%d %d", &a, &b);   
      v.push_back(make_pair(a,b));   
      }   
      lungime=0;   
      sort(v.begin(), v.end());   
      x=v[0].first-1;   
      for (i=0;i<n;i++)   
          {   
          if (v[i].first>x)   
         {   
         lungime+=v[i].second-v[i].first;   
         x=v[i].second;   
         }   
         else  
         if (v[i].second>x)   
            {   
            lungime+=v[i].second-x;   
            x=v[i].second;   
          }   
    }   
printf("%d\n",lungime);   
fflush(stdout);   
return 0;   
}