#include<iostream>
#include<cmath>
#include<cstdio>
#include<string>
using namespace std;

int main()
{
    int h1, m1, h2, m2, n;
    int sleep = 0;

    cin >> n;
    for(int i=0; i<n ;i++){
        scanf("%d:%d %d:%d", &h1, &m1, &h2, &m2);
        if(h1 > h2){
            h1 -= 24;
        }
        if(m2 < m1){
            sleep -= 60;
        }
        sleep += ((60 - m1) + m2)%60;
        sleep += (h2 - h1)*60;
    }
    cout << sleep << endl;

    return 0;
}