long gridlandMetro(long n, long m, int k, vector<vector<int>> track) {
    if (track.empty()) return n * m;
    long lamppost = 0;
    sort(track.begin(), track.end());
    int currentRow = track[0][0], trackCell = 0, lastEnd = 0, rowCounter = 1;
    for (int i=0; i < track.size(); i++) {
        if (track[i][0] != currentRow) {
            lamppost = lamppost + m - trackCell;
            currentRow = track[i][0];
            trackCell = 0;
            lastEnd = 0;
            rowCounter++;
        }
        if (i < track.size()-1 and track[i+1][0] == currentRow and track[i][1] == track[i+1][1]) continue;
        trackCell = trackCell + track[i][2] - track[i][1] + 1;
        trackCell = (track[i][1] <= lastEnd) ? (trackCell - min(lastEnd-track[i][1]+1, track[i][2]-track[i][1]+1)) : trackCell;
        lastEnd = max(lastEnd, track[i][2]);
    }
    lamppost = lamppost + m - trackCell + m * (n - rowCounter);
    return lamppost;
}