#define _USE_MATH_DEFINES

#include <iostream>		//cin, cout
#include <vector>		//vector
#include <algorithm>	//sort,min,max,count
#include <string>		//string,getline, to_string
#include <cstdlib>		//abs(int)
#include <utility>		//swap, pair
#include <deque>		//deque
#include <climits>		//INT_MAX
#include <bitset>		//bitset
#include <cmath>		//sqrt, ceil. M_PI, pow, sin
#include <ios>			//fixed
#include <iomanip>		//setprecision
#include <sstream>		//stringstream
#include <numeric>		//gcd, assumlate
#include <random>		//randam_device
#include <limits>		//numeric_limits

using namespace std;
constexpr long long int D_MOD = 1000000007;

inline vector<string> SplitString(const string& str, const char key) {
	//文字列を任意の文字で分割

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

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

inline vector<int> CalcElapsedTime(int h1, int m1, int h2, int m2) {
	//h1時m1分～h2時m2分の経過時間を計算する

	vector<int> ans(2);
	ans[1] = (m2 - m1 + 60) % 60;
	ans[0] = (h2 - h1 + 24 - (m2 < m1)) % 24;
	return ans;
}

int main() {

	int N;
	cin >> N;

	string temp;
	vector<string> S1, S2;
	vector<int> T(2);

	int ans = 0;

	for (int i = 0; i < N; i++) {
		cin >> temp;
		S1 = SplitString(temp, ':');
		cin >> temp;
		S2 = SplitString(temp, ':');
		T = CalcElapsedTime(stoi(S1[0]), stoi(S1[1]), stoi(S2[0]), stoi(S2[1]));
		ans = ans + T[0] * 60 + T[1];
	}

	cout << ans << endl;

	return 0;

}