#include<stdio.h>
int main(){
  int H,M,h,m,n,s=0;
  scanf("%d",&n);
  while(n--){
    scanf("%d:%d%d:%d",&H,&M,&h,&m);
    h+=H>h?24:H==h&&M>m?24:0; 
    if(M>m){h--;m+=60;}
    s+=(h-H)*60+m-M;
  }
  printf("%d\n",s);
  return 0;
}