/**
	author:  shobonvip
	created: 2024.11.11 02:48:17
**/

#include<bits/stdc++.h>
using namespace std;

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	

	auto parse = [&](string s) -> int {
		int h = 0, m = 0;
		int mode = 0;
		for (char c: s) {
			if (c == ':') {
				mode = 1;
				continue;
			}
			if (mode == 0) {
				h = h * 10 + int(c - '0');
			}else{
				m = m * 10 + int(c - '0');
			}
		}
		return h * 60 + m;
	};

	int t; cin >> t;
	int ans = 0;
	while(t--){
		string s, t; cin >> s >> t;
		int sleep = parse(s);
		int wake = parse(t);
		if (sleep > wake) wake += 1440;
		ans += wake - sleep;
	}
	cout << ans << '\n';
}