#include <iostream>
using namespace std;
int main() {
	int N;
	int H[30], M[30], h[30], m[30];
	int hour = 0, min = 0;
	char token;
	cin >> N;
	for (int i = 0; i < N;i++) {
		cin >> H[i] >> token >> M[i] >> h[i] >> token >> m[i];
	}
	for (int i = 0; i < N;i++) {
		if (H[i] > h[i]) {
			if (M[i] <= m[i]) { min += m[i] - M[i]; hour += (h[i] + 24) - H[i]; continue; }
			else { min += (m[i] + 60) - M[i]; hour += (h[i] + 23) - H[i]; continue; }
		}
		else if(H[i] < h[i]){
			if (M[i] <= m[i]) { min += m[i] - M[i]; hour += h[i] - H[i]; continue; }
			else { min += (m[i] + 60) - M[i]; hour += (h[i] - 1) - H[i]; continue; }
		}
		else {
			if (M[i] <= m[i]) { min += m[i] - M[i]; continue; }
			else { min += (m[i] + 60) - M[i]; hour += 23; continue; }
		}
	}
	cout << hour * 60 + min << endl;
	return 0;
}