#include <bits/stdc++.h>

using namespace std;


int main() {
    int N;
    cin >> N;

    int ans = 0;
    for (int i = 0; i < N; ++i) {
        int h1, m1, h2, m2;
        char c;
        cin >> h1 >> c >> m1 >> h2 >> c >> m2;

        int t = (h2 - h1) * 60 + m2 - m1;
        ans += t;
        if (t < 0) ans += 24 * 60;
    }
    
    cout << ans << endl;
    return 0;
}