#include <stdio.h>

int main(void)
{
	int n,s=0,H,M,h,m,i;
	scanf("%d",&n);
	for(i=0;i<n;i++){
		scanf("%d:%d",&H,&M);
		scanf("%d:%d",&h,&m);
		if(H*60+M>h*60+m)s+=1440-H*60-M+h*60+m;
		else s+=h*60+m-H*60-M;
	}
	printf("%d",s);
	return 0;
}