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

int main() {
    int n, ans = 0;
    cin >> n;
    for (int i = 0; i < n; i++) {
        int h0, m0, h1, m1;
        scanf("%d:%d %d:%d", &h0, &m0, &h1, &m1);
        ans += (60 * h1 + m1 - 60 * h0 - m0 + 86400) % (24 * 60);
    }
    cout << ans << endl;
}