#include<stdio.h>


int main(void){

	int i,n,H[30],M[30],h[30],m[30],sum=0;
	scanf("%d",&n);

	for(i=0;i<n;i++){
		scanf("%d:%d %d:%d",&H[i],&M[i],&h[i],&m[i]);

		if(H[i]>h[i]){
			h[i]=h[i]+24;

		}else if(H[i]==h[i] && M[i]>m[i]){
			h[i]=h[i]+24;
		}

		sum = sum+ (h[i]*60+m[i]) - (H[i]*60+M[i]) ;

//	printf("%d\n",sum);
				
	}

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


//	for(i=0;i<n;i++){
//	printf("%d:%d %d:%d\n",H[i],M[i],h[i],m[i]);
//	}


	return 0;
}