#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
using ll = long long;
using namespace std;
const int INF = 1e9;

int main() {
    int n;
    cin >> n;

    ll ans = 0;
    rep(i, n) {
        int s, e;
        int a, b, c, d;
        scanf("%d:%d %d:%d", &a, &b, &c, &d);

        s = a * 60 + b;
        e = c * 60 + d;

        if (s > e)
            e += 1440;

        ans += e - s;
    }

    cout << ans << endl;

    return 0;
}