#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
using namespace std;
typedef pair<int, int> pii;
#define rep(i,x) for(int i=0;i<(int)(x);i++)

int main(){
	int n, h1, h2, m1, m2, ans = 0;
	char c;
	cin >> n;
	rep(i,n) {
		cin >> h1 >> c >> m1 >> h2 >> c >> m2;
		m1 += h1*60;
		m2 += h2*60;
		ans += m2 - m1;
		if (m2-m1 < 0) ans += 24*60;
	}
	cout << ans << endl;
	return 0;
}