#include<stdio.h>
int main()
{
	int val;
	scanf("%d", &val);
	int startH, startM, finishH, finishM;
	int ans = 0;
	for (int i = 0; i < val; i++)
	{
		scanf("%d:%d %d:%d", &startH, &startM, &finishH, &finishM);
		startM += 60 * startH;
		finishM += 60 * finishH;
		if (startM > finishM)
			finishM += 24 * 60;
		ans += finishM - startM;
	}
	printf("%d\n", ans);
	return 0;
}