Does anyone have any suggestions on how to do it in excel?

There is a list of odd numbers under A column
1,3,5,7,9,...
When I input any number in cell B1, such as 7.8, then it should return 7 in
cell C1, because 7.8 is closer to 7 than 9.
When I input any number in cell B1, such as 8.1, then it should return 9 in
cell C1, because 8.1 is closer to 9 than 7.
When I input any number in cell B1, such as 8, then it should return 7 in
cell C1, because it is my preference.
Does anyone have any suggestions?
Thanks in advance for any suggestions
Eric