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

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