#include <stdio.h>

void main(void){
	int n;
	scanf("%d",&n);
	int sleepH,sleepM,occurH,occurM,sleepTime = 0;
	for(int i = 0 ; i < n ; i ++ ){
		scanf("%d:%d %d:%d",&sleepH,&sleepM,&occurH,&occurM);
		if(occurH-sleepH > 0){
		sleepTime += (occurH*60+occurM)-(sleepH*60+sleepM);
		}else{
			sleepTime += (occurH*60+occurM+1440)-(sleepH*60+sleepM);
		}
	}
	printf("%d",sleepTime);
}