#include<iostream>
#include<string>
#include<string.h>
#include<algorithm>
#include<stdio.h>
#include<cmath>
#include<vector>
#include<utility>
#include<stack>
#include<queue>
#include<list>
#include<bitset>

#define FOR(i, a, b) for(int i=(a);i<=(b);i++)
#define RFOR(i, a, b) for(int i=(a);i>=(b);i--)
#define MOD 1000000007
#define INF 1000000000

using namespace std;


int main(void) {
	int n;
	int total = 0;
	
	cin >> n;
	FOR(i, 1, n) {
		int a, b, c, d;
		int be, af;
		scanf("%d:%d", &a, &b);
		scanf("%d:%d", &c, &d);
		be = a * 60 + b;
		af = c * 60 + d;
		if (be > af) {
			total += (af + 1440) - be;
		}
		else {
			total += af - be;
		}
	}
	cout << total << endl;
	return 0;
}