使用Python编写一个计时器程序，并在暂停时添加一秒。

示例代码：

import time

class Timer:
    def __init__(self):
        self.start_time = None
        self.paused_time = None
        self.paused = False
        self.pause_duration = 0
    
    def start(self):
        if not self.start_time:
            self.start_time = time.time()
        elif self.paused:
            self.pause_duration += time.time() - self.paused_time
            self.paused = False
    
    def pause(self):
        if not self.paused:
            self.paused_time = time.time()
            self.paused = True
    
    def reset(self):
        self.start_time = None
        self.paused_time = None
        self.paused = False
        self.pause_duration = 0
    
    def elapsed_time(self):
        if self.start_time:
            if self.paused:
                return self.paused_time - self.start_time + self.pause_duration
            else:
                return time.time() - self.start_time + self.pause_duration
        return 0

timer = Timer()
timer.start()
time.sleep(5)
timer.pause()
time.sleep(1)
timer.start()
time.sleep(3)
print(timer.elapsed_time())