#include<iostream>
#include<string>
#include<math.h>
using namespace std;

int main(){
	int n;
	int a,b;
	int H, h, M, m;
	int dh, dm;
	int ans = 0;
	string s1;
	string s2;
	cin >> n;
	for (int i = 0; i < n; i++){
		cin >> s1;
		cin >> s2;
		a = s1.find(":");
		if (a == 1){
			H = s1[0] - '0';
			if (s1[3] == '\0'){
				M = s1[2] - '0';
			}
			else{
				M = (s1[2] - '0') * 10 + (s1[3] - '0');
			}
		}
		else{
			H = (s1[0] - '0') * 10 + (s1[1] - '0');
			if (s1[4] == '\0'){
				M = s1[3] - '0';
			}
			else{
				M = (s1[3] - '0') * 10 + (s1[4] - '0');
			}
		}
		b = s2.find(":");
		if (b == 1){
			h = s2[0] - '0';
			if (s2[3] == '\0'){
				m = s2[2] - '0';
			}
			else{
				m = (s2[2] - '0') * 10 + (s2[3] - '0');
			}
		}
		else{
			h = (s2[0] - '0') * 10 + (s2[1] - '0');
			if (s2[4] == '\0'){
				m = s2[3] - '0';
			}
			else{
				m = (s2[3] - '0') * 10 + (s2[4] - '0');
			}
		}
		dh = h - H;
		dm = m - M;
		if (dm < 0){
			dm += 60;
			dh -= 1;
		}
		if (dh < 0){
			dh += 24;
		}

		ans += dh * 60 + dm;
	}
		cout << ans << endl;

	






	return 0;
}