#include <string>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <list>
#include <stdexcept>
#include <functional>
#include <utility>
#include <iomanip>
#include <ctime>
#include <valarray>
#include <iostream>
#include <sstream>
#include <fstream>
using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
#define MEM(a,b) memset((a),(b),sizeof(a))
const LL INF = 1e9 + 7;
const int N = 2e5 + 10;

int main()
{
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);
	int ans = 0;
	int n;
	scanf("%d", &n);
	while (n--)
	{
		int h1, m1, h2, m2;
		scanf("%d:%d %d:%d", &h1, &m1, &h2, &m2);
		int d = (h2 - h1) * 60 + (m2 - m1);
		if (d < 0) d += 24 * 60;
		ans += d;
	}
	cout << ans << endl;

	return 0;
}