#include <iostream>
#include <sstream>
#include <math.h>
#include <stack>
#include <set>
#include <algorithm>
#include <string>
#include <queue>
#include <stack>
#include <map>
#include <cstdio>
#include <vector>
using namespace std;

#define INF (1 << 30)
#define INFLL (1LL << 60)

int main() {
	int sum = 0;
	int a,b,c,d,n;
	char koro;
	cin >> n;
	for(int i = 0;i < n;i++){
		cin >> a >> koro >> b >> c >> koro >> d;
		if(a > c ) sum += (24*60 - (a*60 + b)) + c*60 + d;
		else sum += (c*60 + d) - a*60 - b;
	}
	cout << sum << endl;
	return 0;
}