#include<iostream>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<cmath>
using namespace std;
int main(){
    long long sum=0;
    int N,i,H,M,h,m;
    cin >> N;
    for(i=0;i<N;i++){
        scanf("%d:%d %d:%d",&H,&M,&h,&m);
        if(H>h){

            sum += ((24-H+h)*60+(m-M));
        }
        else if(H==h){
            if(M>m){
                sum += ((h-H)*60+(m-M));
            }
            else{
                sum += ((24-H+h)*60+(m-M));
            }
        }
        else{
            sum += ((h-H)*60+(m-M));
        }
    }
    cout << sum;
    return 0;
}