#include <iostream>	//cin, cout
#include <vector>	//vector
#include <algorithm> //sort,min,max
#include <string>	//string
#include <ios>		//fixed
#include <iomanip>	//setprecision
#include <utility> //swap
#include <cstdlib>	//abs(int)
#include <sstream>	//stringstream,getline

using namespace std;

inline vector<string> Split_String(const string& str, const char key) {

	vector<std::string> result;
	stringstream SS(str);
	string temp;

	while (getline(SS, temp, key)) {
		result.push_back(temp);
	}

	return(result);
}

int main() {

	int N;
	cin >> N;

	string temp;
	vector<string> A, B;

	int h = 0, m = 0;

	for (int i = 0; i < N; i++) {
		cin >> temp;
		A = Split_String(temp, ':');
		cin >> temp;
		B = Split_String(temp, ':');

		h += (stoi(B[0]) + 24 - stoi(A[0])) % 24;
		if (stoi(B[1]) < stoi(A[1])) {
			h--;
			if (h < 0) {
				h = 23;
			}
		}
		m += (stoi(B[1]) + 60 - stoi(A[1])) % 60;
	}

	cout << h * 60 + m << endl;

	return 0;

}