------
## 最终结论
```python
def carFleet(target, position, speed):
    cars = sorted(zip(position, speed), reverse=True)
    times = [(target - p) / s for p, s in cars]
    fleets = 0

    while len(times) > 1:
        lead_time = times.pop(0)
        if lead_time < times[0]:
            fleets += 1
        else:
            times[0] = lead_time

    return fleets + bool(times)

# Example usage
target = 12
position = [10,8,0,5,3]
speed = [2,4,1,1,3]
print(carFleet(target, position, speed))  # Output: 3
```