#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
#define rep(i, n) REP(i, 0, n)
#define REP(i, s, e) for (ll i = (s); i < (ll)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for (ll i = (ll)(s - 1); i >= (ll)(e); i--)
#define all(r) r.begin(), r.end()
#define rall(r) r.rbegin(), r.rend()

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;

template <typename T, typename U>
bool chmax(T& a, const U& b) {
    if (a >= b) return false;
    a = b;
    return true;
}
template <typename T, typename U>
bool chmin(T& a, const U& b) {
    if (a <= b) return false;
    a = b;
    return true;
}

void yes_no(bool f, string yes = "Yes", string no = "No") {
    cout << (f ? yes : no) << "\n";
}

vector<string> split_string(const string& s, char c = ' ') {
    vector<string> res;
    stringstream ss(s);
    string tmp;
    while (getline(ss, tmp, c)) {
        res.emplace_back(tmp);
    }
    return res;
}

void solve() {
    int n;
    cin >> n;
    ll ans = 0;
    rep(i, n) {
        string s, t;
        cin >> s >> t;
        auto f = [](string s) {
            auto t = split_string(s, ':');
            ll res = atol(t[0].c_str()) * 60;
            res += atol(t[1].c_str());
            return res;
        };
        ll a = f(s), b = f(t);
        ll tmp = b - a;
        if (tmp < 0) tmp += 24 * 60;
        ans += tmp;
    }
    cout << ans << "\n";
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int t = 1;
    // cin >> t;
    rep(ti, t) solve();
    return 0;
}