Some rectangular sheets of paper, all the same size, are placed in a pile. The pile is then folded in half to form a booklet. The pages are then numbered in order 1, 2, 3, 4, $\cdots$ from the first page to the last page. On one of the sheets, the sum of the numbers on the four pages is 58.  How many sheets of paper were there at the start? 
Overseas Competition->Knowledge Point->Word Problem Modules->Page Number Problem