#include<stdio.h>
#include<stdlib.h>
int main(){
  int h1,m1,h2,m2,n,sum=0;
  scanf("%d",&n);
  while(n--){
    scanf("%d:%d%d:%d",&h1,&m1,&h2,&m2);
    h2+=h1>h2?24:m1>m1?24:0; 
    if(m1>m2){h2--;m2+=60;}
    sum+=(h2-h1)*60+m2-m1;
  }
  printf("%d\n",sum);
  return 0;
}