#include <iostream>
#include <algorithm>

using namespace std;

int main() {
    int n;
    int total;
    
    cin >> n;
    
    for (int i = 0; i < n; i++) {
        string start;
        string end;
        
        cin >> start >> std::ws >> end;
        
        string tm;
        int stt;
        for (int j = 0; j < start.length(); j++) {
            if (start[j] == ':') {
                stt = 60 * stoi(tm);
                tm = "";
            } else {
                tm += start[j];
            }
        }
        stt += stoi(tm);
        
        tm = "";
        int nd;
        for (int k = 0; k < end.length(); k++) {
            if (end[k] == ':') {
                nd = 60 * stoi(tm);
                tm = "";
            } else {
                tm += end[k];
            }
        }
        nd += stoi(tm);
        
        if (nd > stt) {
            total += nd - stt;
        } else {
            total += (60 * 24 - stt) + nd;
        }
    }
    
    cout << total << endl;
    
    return 0;
}