At the close of every election by ballot, the judges shall proceed publicly to canvass the votes, which canvass when commenced must continue without adjournment or interruption until the same is completed. The canvass must be conducted by taking one ballot at a time from the ballot box and counting until the number of ballots is equal to the number of names on the poll list, and if there are any left in the box, they must be destroyed immediately. If on the opening of the ballots, two or more ballots are found to be so folded that it is apparent that the same person voted them, the board shall destroy such unlawful ballots immediately. The person having the greatest number of votes for an office must be declared elected.