/*
#include <bits/stdc++.h>
#define INT long long int
#define mod 1000000007
using namespace std;
int n;
long long s = -987654321987, e = -978654321987, ans;
pair<long long, long long> a[1000100];
set<long long int> S;
int main()
{
    ios::sync_with_stdio(false);
    //freopen(".17.in","r",stdin);
    cin>>n;
    for(int i = 0 ; i< n ; i++ )
    {
        cin>>a[i].first>>a[i].second;
        for(int j = a[i].first+1 ; j <= a[i].second ; j++ )
           S.insert(j);
    }
    cout<<S.size()<<endl;
}
*/

#include <bits/stdc++.h>

using namespace std;
int n;
long long s = -987654321987, e = -978654321987, ans;
bool flag = false;
pair<long long, long long> a[1000100];
int main()
{
    ios::sync_with_stdio(false);
    freopen(".20.in","r",stdin);
    freopen(".20.out","w",stdout);
    cin>>n;
    for(int i = 0 ; i< n ; i++ ) cin>>a[i].first>>a[i].second;
    sort(a, a+n);
    s = a[0].first, e = a[0].second;
    for(int i = 1 ; i < n ; i++ )
    {
        if( a[i].first <= a[i-1].second ) e = max( e, a[i].second ), flag = false;
        else ans += e-s, s = a[i].first, e = a[i].second, flag = true;
    }
    if( !flag ) ans += e-s;
    cout<<ans<<endl;
}