ds = [43, 23, 40, 13]
idx = 4
"(0)----43----(1)----23----(2)----40----(3)----13----(4)"
def solve(distances, missing_index):
    num_stations = len(distances)
    station_idx, rider_distance, num_riders = 0, 0, 1
    done = False
    while station_idx < num_stations:
        if rider_distance + distances[station_idx] <= 100:
            if station_idx + 1 == missing_index - 1 and not done:
                num_riders += 1 
                rider_distance = distances[station_idx]
                done = True
                print("missing")
            else:
                rider_distance += distances[station_idx]
                station_idx += 1
                print("move on")
        else:
            num_riders += 1
            rider_distance = 0
            print("new rider!")
        print(station_idx, rider_distance, num_riders)
    return num_riders

r = solve(ds, idx)
print(r)