#include <stdio.h>

int main()
{
	int N, sum = 0;

	if (scanf("%d", &N) != 1) {
		return 1;
	}

	for (int i = 0; i < N; i++) {
		int H, M, h, m, in, out;
		if (scanf("%d:%d %d:%d", &H, &M, &h, &m) != 4) {
			return 1;
		}

		in = H * 60 + M;
		out = h * 60 + m;

		if (out < in) {
			out += 24 * 60;
		}

		sum += out - in;
	}

	printf("%d", sum);
	
	return 0;
}