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

int minuites(string s) {
    int m = 0, h = 0;
    bool flag = false;
    for (auto& c : s) {
        if (c == ':') {
            flag = true;
            continue;
        }
        if (flag) {
            m *= 10;
            m += c - '0';
        } else {
            h *= 10;
            h += c - '0';
        }
    }
    return h * 60 + m;
}

int main() {
    int N, slept = 0;
    cin >> N;

    while (N--) {
        string s1, s2;
        cin >> s1 >> s2;
        int sleep = minuites(s1), wake = minuites(s2);
        if (sleep > wake) wake += 24 * 60;
        slept += wake - sleep;
    }
    cout << slept << endl;
}