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

int n, ans;
int h1, m1, h2, m2;

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