#include<stdio.h>
#include<string.h>

int main(void){
	int n,i,hs,ms,hf,mf,r = 0;
	scanf("%d",&n);
	for(i = 1;i <= n;i++){
		scanf("%d:%d %d:%d",&hs,&ms,&hf,&mf);
		ms+=(hs*60);
		mf+=(hf*60);
		if(mf < ms){mf+=1440;}
		r+=(mf-ms);
	}
	printf("%d\n",r);
	return 0;
}