#define  _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <algorithm>
#include <utility>
#include <functional>
#include <cstring>
#include <queue>
#include <stack>
#include <math.h>
#include <iterator>
#include <vector>
#include <string>
#include <set>
#include <math.h>
#include <iostream> 
#include <random>
#include<map>
#include <iomanip>
#include <time.h>
#include <stdlib.h>
#include <list>
#include <typeinfo>
#include <list>
#include <set>
#include <cassert>
#include<fstream>
#include <unordered_map>  
using namespace std;
#define eps 0.00000001
#define LONG_INF 10000000000000000
#define GOLD 1.61803398874989484820458
#define MAX_MOD 1000000007
#define REP(i,n) for(long long i = 0;i < n;++i)
int main() {
	int n;
	cin >> n;
	int ans = 0;
	REP(i, n) {
		int c[2] = {};
		for (int q = 0;q < 2;++q) {
			int a, b;
			scanf("%d:%d", &a, &b);
			c[q] = a * 60 + b;
		}
		if (c[0] > c[1]) {
			ans += 1440 - (c[0] - c[1]);
		}
		else {
			ans += c[1] - c[0];
		}
	}
	cout << ans << endl;
	return 0;
}