gridland metro

ans = n*m
    cnt = 0
    dic={}
    for i in range(len(track)):
        if track[i][0] not in dic:
            dic[track[i][0]] = [track[i][1]]
            dic[track[i][0]].append(track[i][2])
        else:
            if(track[i][1]<=max(dic[track[i][0]])):
                dic[track[i][0]].append(track[i][1])
                dic[track[i][0]].append(track[i][2])
            else:
                cnt+=track[i][1]-max(dic[track[i][0]])-1
                dic[track[i][0]].append(track[i][1])
                dic[track[i][0]].append(track[i][2])
                
    print(dic)
    sm=0
    for i in dic:
        m = max(dic[i])
        n = min(dic[i])
        sm+=m-n+1
    return ans-sm+cnt