#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0, i##_len = (n); i < i##_len; i++)
#define reps(i, s, n) for(ll i = (s), i##_len = (n); i < i##_len; i++)
#define rrep(i, n) for(ll i = (n) - 1; i >= 0; i--)
#define rreps(i, e, n) for(ll i = (n) - 1; i >= (e); i--)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())
#define len(x) ((ll)(x).length())

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    // ifstream in("input.txt");
    // cin.rdbuf(in.rdbuf());
    ll n;
    cin >> n;
    ll ans = 0;
    rep(i, n) {
        string in, out;
        cin >> in >> out;
        ll p = 0;
        vector<ll> inv(2, 0);
        rep(ii, len(in)) {
            if (in[ii] == ':') {
                p++;
            }
            else {
                inv[p] = inv[p] * 10 + (in[ii] - '0');
            }
        }
        p = 0;
        vector<ll> outv(2, 0);
        rep(ii, len(out)) {
            if (out[ii] == ':') {
                p++;
            }
            else {
                outv[p] = outv[p] * 10 + (out[ii] - '0');
            }
        }
        ll inm = inv[0] * 60 + inv[1];
        ll outm = outv[0] * 60 + outv[1];
        ans += (24 * 60 + outm - inm) % (24 * 60);
    }
    cout << ans << endl;
    return 0;
}