#include <bits/stdc++.h>
using namespace std;
 
int main(){
   int N;
    cin>>N;
   int H,M,h,m;
   char gomi1,gomi2;
   int sum=0;
   for(int i=0;i<N;i++){
       cin>>H>>gomi1>>M; cin>>h>>gomi2>>m;
       int minute1=60*H+M;
       int minute2=60*h+m;
       int d=minute2-minute1;
       if(d>0){
           sum+=d;
       }
       else if(d<0){
           sum+=(1440-minute1+minute2);
       }
       
   }
   cout<<sum<<endl;
}