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

class Time {
   private:
    int seconds;
    void mod() {
        seconds %= 60 * 60 * 24;
        seconds += 60 * 60 * 24;
        seconds %= 60 * 60 * 24;
    }

   public:
    Time(const int& seconds) : seconds(seconds) {
        mod();
    }

    Time(const int& h, const int& m, const int& s) {
        seconds = h * 60 * 60 + m * 60 + s;
        mod();
    }

    int hour() {
        return seconds / (60 * 60);
    }

    int minute() {
        return (seconds % (60 * 60)) / 60;
    }

    int second() {
        return seconds % 60;
    }

    Time operator+(const Time& t) {
        return Time(this->seconds + t.seconds);
    }

    Time operator-(const Time& t) {
        return Time(this->seconds - t.seconds);
    }

    void operator+=(const Time& t) {
        this->seconds += t.seconds;
        mod();
    }

    void operator-=(const Time& t) {
        this->seconds -= t.seconds;
        mod();
    }
};

int main() {
    int N;
    cin >> N;
    int H, M, h, m;
    char _;
    long long ans = 0;
    for (size_t i = 0; i < N; i++) {
        cin >> H >> _ >> M >> h >> _ >> m;
        Time diff = Time(h, m, 0) - Time(H, M, 0);
        ans += diff.hour() * 60 + diff.minute();
    }
    cout << ans << endl;
}