#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <climits>
#include <string>
#include <set>
#include <cmath>
#include <map>
#include <unordered_map>
#include <numeric>
#include <random>
#include <memory>
#include <chrono>
#include <iterator>
#include <functional>
#include <unordered_set>
#include <cassert>
#ifdef LOCAL
#include "debug.h"
#else
#define debug(x...)
#endif
//#pragma GCC optimize("Ofast")
//#define int ll



using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair <int, int> pii;
#define mp make_pair
#define pb push_back
#define sz(x) int((x).size())

#ifndef LOCAL
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#else
mt19937 rng(228);
#endif

const int N = 2e3 + 7;
const int inf = INT_MAX / 2;
const ll INF = LLONG_MAX / 3;
const int MOD = 1e9 + 7;
const double eps = 1e-6;
const string cars[] = {"🚗", "🚕", "🚙"};


signed main() {
#ifdef LOCAL
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    cout << fixed << setprecision(9);
    ios::sync_with_stdio(false);
    cin.tie();
    cout.tie();

    int n;
    cin >> n;
    int r = n;

    vector < pii > a;

    for (int i = 0; i < n; i++) {
        int h, m, s;
        cin >> h >> m >> s;
        int start = s + m * 60 + h * 3600;

        cin >> h >> m >> s;
        int finish = s + m * 60 + h * 3600;

        if (start == finish) {
            r--;
        }
        else {
            if (start > finish) {
                a.push_back({ start, 1 });
                a.push_back({ 60 * 60 * 24, -1 });

                a.push_back({ 0, 1 });
                a.push_back({ finish, -1 });
            }
            else {
                a.push_back({ start, 1 });
                a.push_back({ finish, -1 });
            }

        }
    }

    sort(a.begin(), a.end(), [](auto x, auto y) {
        if (x.first != y.first) {
            return x.first < y.first;
        }
        return x.second > y.second;
    });

    int b = 0, ans = 0;
    for (int i = 0; i < sz(a); i++) {
        b += a[i].second;

        if (b == r) {
            ans += a[i + 1].first - a[i].first;
        }
    }

    cout << ans;

    return 0;
}