#55405: c++ vector解
#include <bits/stdc++.h>
using namespace std;
int main(){
int n,a,b;
cin>>n;
vector <pair<int,int>> v;
while(n--){
cin>>a>>b;
v.push_back({a,b});}
sort(v.begin(),v.end());
int total=0,low=v[0].first,high=v[0].second;
for(int i=1;i<v.size();i++){
if(v[i].first<=high){
high=max(high,v[i].second);
}else{
total+=high-low;
low=v[i].first;high=v[i].second;
}}
cout<<total+high-low<<endl;
return 0;
}