#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <fstream>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>
#include <iterator>

typedef long long int ll;
//#include<bits/stdc++.h>


using namespace std;





int main()
{

    int Q;
    Q = 1;
    //cin >> Q;


    while (Q--) {
        int n;
        cin >> n;
        int ans = 0;
        for (int i = 0; i < n; i++) {
            string a, b;
            cin >> a >> b;

            int d = 0;
            int x = 0, y = 0;
            for (int i = 0; i < a.size(); i++) {
                if (a[i] == ':') {
                    x = d * 60; d = 0;
                }
                else {
                    d *= 10;
                    d += a[i] - '0';
                }
            }
            x += d; d = 0;

            for (int i = 0; i < b.size(); i++) {
                if (b[i] == ':') {
                    y = d * 60; d = 0;
                }
                else {
                    d *= 10;
                    d += b[i] - '0';
                }
            }

            y += d;
            if (y > x)ans += y - x;
            else {
                ans += 24 * 60 - (x - y);
            }

        }
        
        cout << ans;
    }
    return 0;
}