#define _USE_MATH_DEFINES	//M_PI
#include <iostream>			//std::cout, std::cin
#include <string>			//std::string
#include <vector>			//std::vector
#include <valarray>			//std::valarray	数値のみの一次配列
#include <algorithm>		//std::sort
#include <time.h>			//localtime_s
#include <cstdlib>			//abs
#include <cmath>			//abs, std::pow, sqrt, sin, cos,
#include <fstream>			//std::ifstream
#include <iomanip>			//std::setprecision
#include <random>			//std::random(C++11)
#include <numeric>			//std::accumulate

int main(void) {

	
	//test用
	//std::ifstream in("test.txt");
	//std::cin.rdbuf(in.rdbuf());

	int N;
	std::string str1, str2;
	std::cin >> N;

	int ans = 0;
	for (int i = 0; i < N; i++) {

		std::cin >> str1 >> str2;

		std::string temp;
		int s_h, s_m, w_h, w_m;
		
		int j = 0;
		while (str1[j] != ':') {
			temp.push_back(str1[j]);
			j++;
		}
		s_h = std::stoi(temp);

		j++;
		temp.clear();
		while (j < str1.length()) {
			temp.push_back(str1[j]);
			j++;
		}
		s_m = std::stoi(temp);

		j = 0;
		temp.clear();
		while (str2[j] != ':') {
			temp.push_back(str2[j]);
			j++;
		}
		w_h = std::stoi(temp);

		j++;
		temp.clear();
		while (j < str2.length()) {
			temp.push_back(str2[j]);
			j++;
		}
		w_m = std::stoi(temp);

		if (s_h > w_h) {
			ans += (24 - s_h - 1) * 60 + (60 - s_m) + w_h * 60 + w_m;
		}
		else if (s_h < w_h) {
			ans += (w_h - s_h - 1) * 60 + (60 - s_m) + w_m;
		}
		else {
			if (w_m >= s_m) {
				ans += w_m - s_m;
			}
			else {
				ans += 23 * 60 + (60 - s_m) + w_m;
			}
		}
	}

	std::cout << ans << std::endl;
}