#include<stdio.h>
#include<stdlib.h>

int main(void){

	int n;

	scanf("%d",&n);

	int **time;
	int count = 0;
	int check = 0;

	time = malloc(sizeof(int *)*n);

	for(int i = 0;i < n;i++){
		time[i] = malloc(sizeof(int) * 4);
	}

	for(int i = 0;i < n;i++){
		scanf("%d:%d",&time[i][0],&time[i][1]);
		scanf("%d:%d",&time[i][2],&time[i][3]);
	}

	for(int i = 0;i < n;i++){

		check = 0;

		if(time[i][1] > time[i][3]){
			check = 1;
			count += time[i][3]+60-time[i][1];
		}else{
			count += time[i][3]-time[i][1];
		}

		if(check == 1){
			if(time[i][0] > time[i][2]){
				count += (time[i][2]+24-1-time[i][0])*60;
			}else{
				count += (time[i][2]-1-time[i][0])*60;
			}
		}else{
			if(time[i][0] > time[i][2]){
				count += (time[i][2]+24-time[i][0])*60;
			}else{
				count += (time[i][2]-time[i][0])*60;
			}
		}

	}

	printf("%d\n",count);

	for(int i = 0;i < n;i++){
		free(time[i]);
	}
	free(time);
	return 0;
}