No such file or directory: 'result/cg.dot'

[mitmul]

I got this error after clicking Run button in the page Chainerの基本：MNIST 例

Traceback (most recent call last):
  File "/var/sandbox/main.py", line 73, in <module>
    trainer.run()
  File "/usr/local/lib/python2.7/dist-packages/chainer/training/trainer.py", line 269, in run
    entry.extension(self)
  File "/usr/local/lib/python2.7/dist-packages/chainer/training/extensions/computational_graph.py", line 57, in dump_graph
    with open(out_path, 'w') as f:
IOError: [Errno 2] No such file or directory: 'result/cg.dot'
�[J
Program exited.