#include <iostream>
using namespace std;

int main() {
    int n, ans = 0;
    cin >> n;
    for (int i = 0; i < n; i++) {
        char colon;
        int h1,m1,h2,m2;
        cin >> h1 >> colon >> m1 >> h2 >> colon >> m2;
        ans += (h2 * 60 + m2 - h1 * 60 - m1 + 24 * 60) % (24 * 60);
    }
    cout << ans << endl;
    return 0;
}