Add the number of days in January March, April, May, June, July, August, September, October, November and December. 
Overseas Competition->Knowledge Point->Word Problem Modules->Periodic Problems->Periodic Problems of Time
The only missing month is February. The sum will be either $$365$$ - $$28$$ or (in leap years) $$366$$ - $$29$$. Both are equal to $$337$$． 