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

int getminute(string s){
	int ret = 0;
	int now = 0;
	for (int i = 0; i < s.size(); i++)
	{
		if (s[i] == ':'){
			ret += now * 60;
			now = 0;
		}
		else{
			now *= 10;
			now += s[i] - '0';
		}
	}
	ret += now;
	return ret;
}

int main(){
	int ans = 0;
	int N;
	cin >> N;
	for (int t = 0; t < N; t++)
	{
		string s1, s2;
		cin >> s1 >> s2;
		int sum = 0;
		sum = getminute(s2) - getminute(s1);
		while (sum < 0) sum += 60 * 24;
		ans += sum;
	}
	cout << ans << endl;
}