# [Python 2], 102 bytes

<!-- language-all: lang-python -->

    n=input()
    r=[a*-~a/2for a in range(n+1)]
    print[(a,b,c)for a in r for b in r for c in r if a+b+c==n][0]

[Try it online!][TIO-j5880e57]

[Python 2]: https://docs.python.org/2/
[TIO-j5880e57]: https://tio.run/##RcqhDoAgEADQzldcBMGpdL6EEQ4mSjkYw2Dx13HOQHvhlbudmXTvZBKVq3HBqrE4zQ8uOuYKCImgIh07J7kJx0pN1CxH5VUQY8BHPxh@pggovQzGkLOr6/0F "Python 2 – Try It Online"