#include <bits/stdc++.h>

#define show(x) cout << #x << " = " << x << endl

using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    os << "sz=" << v.size() << "\n[";
    for (const auto& p : v) {
        os << p << ",";
    }
    os << "]\n";
    return os;
}

template <typename S, typename T>
ostream& operator<<(ostream& os, const pair<S, T>& p)
{
    os << "(" << p.first << "," << p.second
       << ")";
    return os;
}


constexpr ll MOD = 1e9 + 7;

template <typename T>
constexpr T INF = numeric_limits<T>::max() / 100;

int main()
{
    int N;
    cin >> N;
    ll sum = 0;
    for (ll i = 0; i < N; i++) {
        string s[2];
        cin >> s[0] >> s[1];
        string tim_string[2][2];
        for (int j = 0; j < 2; j++) {
            int ind = 0;
            for (int p = 0; p < s[j].size(); p++) {
                if (s[j][p] == ':') {
                    ind++;
                    continue;
                }
                tim_string[j][ind].push_back(s[j][p]);
            }
        }
        const int start = stoi(tim_string[0][0]) * 60 + stoi(tim_string[0][1]);
        const int end = stoi(tim_string[1][0]) * 60 + stoi(tim_string[1][1]);
        sum += (end >= start) ? end - start : end + 1440 - start;
    }
    cout << sum << endl;
    return 0;
}