#include <iostream>
#include <math.h>
#include <algorithm>
#include <functional>
#include <vector>
#include <typeinfo>
#include <climits>
#include <ctype.h>
#include <string>
#include <stdio.h>
using namespace std;
#define INIT cin.tie(0); ios::sync_with_stdio(false);
#define FOR(i, a, n) for (int i = a; i < n; i++)
#define REP(i, n) for(int i = 0; i < n; i++)

int main()
{
    INIT;

    int n;
    cin >> n;

    int total = 0;
    REP(i, n){
        int h1, m1, h2, m2, a, b;
        char c;
        cin >> h1 >> c >> m1 >> h2 >> c >> m2;
        a = h1 * 60 + m1;
        b = h2 * 60 + m2;
        if(a > b) b += 24 * 60;
        total += b - a;
    }
    cout << total << endl;

    return 0;
}