#include "bits/stdc++.h"
using namespace std;

#define REP(i, n) for(int i=0; i<(n); i++)

int N, H, M, h, m;
signed main()
{
    cin >> N;
    int ret = 0;
    REP(i,N) {
        scanf("%d:%d %d:%d", &H, &M, &h, &m);
        int hour = (24 + h - H) % 24;
        int min = (60 + m - M) % 60;
        if (m < M) {
            hour--;
        }
        ret += hour * 60 + min;
    }
    cout << ret << endl;
    return 0;
}