#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
 
vector < pair<int, int> > point;
 
int main(){
    int N,M;
    cin >> N;
    for (int i=0; i < N; i++){
        cin >> M;
        for (int j=0;j < M;j++){
            int x,y;
            cin >> x >> y;
            point.push_back( make_pair(x,-1) );
            point.push_back( make_pair(y, 1) );
        }
    }
    sort (point.begin(), point.end() );
    int open = 0;
    int sum = 0;
    int prev = 0;
    for (auto x : point){
         if (open == N)
            sum += x.first - prev; 
         open -= x.second;
         if (open == N)
            prev = x.first; 
     }
    cout << sum;
}

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MwoxIDMwIDgwCjIgMCAyMCA1MCA5MAoyIDc1MCA3OTUgOTcyIDk4Mg==

3
1 30 80
2 0 20 50 90
2 750 795 972 982