//
//  main.cpp
//  GenirationThePassOnOlymp
//
//  Created by Kadir Kadyrov on 9/23/19.
//  Copyright © 2019 Kadir Kadyrov. All rights reserved.
//

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <set>
#include <cmath>
#include <string.h>
#include <cstdlib>
#include <fstream>
#include <map>
#define N 101
#define MOD 1000000007
#define LOCAL
#undef LOCAL

using namespace std;

int st[25], fn[25];

int main () {

#ifndef LOCAL
    freopen("shop.in", "r", stdin);
    freopen("shop.out", "w", stdout);
#endif

    int n;
    cin >> n;

    for(int i = 0; i < n; i++) {
        int start, finish;
        cin >> start >> finish;
        if(start >= finish) {
            fn[24]++;
            st[start]++;
            st[0]++;
            fn[finish]++;
        } else {
            fn[finish]++;
            st[start]++;
        }
    }

    int num, ans;
    num = ans = 0;
    for(int time = 0; time <= 24; time++) {
        num += st[time];
        num -= fn[time];

        if(num == n)
            ans++;
    }

    cout << ans << endl;



}