思考题 within 5 min

Bomb defusing

「Readers, please set up a 5-minute timer before you continue to read」
Green boy envied Orange Boy for having such a high rating. So he decided to send Orange Boy a present: a bomb! The bomb will explode in 5 minutes!
There's a note:「Orange Boy, I have sent you a bomb. You need to finish the following problem in 5 minutes and program it on the bomb to defuse it. Wanna try? Hahahahaha......」
The problem goes as follows:

**Holiday**
I love holidays with one day more. Please find such an integer x(x>=a,a is given) so that the Sept.1st of year x is Sunday or Saturday
1000<=a<=9999
**Example**
a=2017
out=2018
Explain:
Sept.1st.2017 is Friday
Sept.1st.2018 is Saturday

Be quick orange boy!!!