#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <map>
#include <list>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <iomanip>
#define INF 1050000000

using namespace std;


int main(void)
{
	int n;
	int H, M, h, m;
	char buf[50];
	int sum = 0;

	cin >> n;

	

	for (int i= 0; i < n; i++) {	
		scanf("%s", buf);
		for (int j = 0; j < 50; j++) {
			if (buf[j] == ':') buf[j] = ' ';
		}
		sscanf(buf, "%d %d", &H, &M);
		scanf("%s", buf);
		for (int j = 0; j < 50; j++) {
			if (buf[j] == ':') buf[j] = ' ';
		}
		sscanf(buf, "%d %d", &h, &m);
		
		sum += ((h-H)*60 + (m-M) + 24 * 60) % (24*60);

	}
	cout << sum << endl;
		
	return (0);
}