#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <functional>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cctype>
#include <string>
#include <cstring>

using namespace std;

typedef long long ll;


int main() {
  int n;
  cin >> n;
  int sum = 0;
  for (int i = 0; i < n; i++) {
    int H, M, h, m;
    scanf ("%d:%d %d:%d", &H, &M, &h, &m);

    int s, e;
    s = H*60+M; e = h*60+m;
    if (e > s) {
      sum += e-s;
    }else {
      sum += 60*24-(s-e);
    }
  }

  cout << sum << endl;
}