#include <bits/stdc++.h>

using namespace std;

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

    int ans = 0;

    while (N--) {
        int H, M, h, m; scanf("%d:%d %d:%d", &H, &M, &h, &m);
        if (H * 60 + M > h * 60 + m) h += 24;
        ans += (h * 60 + m) - (H * 60 + M);
    }

    cout << ans << endl;
}