题目

A woman was caught trying to get her boyfriend out of Puente Ayala prison by packing him in a large suitcase. They almost got away with it, but guards became suspicious after seeing the woman struggling with the suitcase. 25-year-old Souda arrived at the Puente Ayala prison in Barcelona, Venezuela, last weeks, to visit her boyfriend, Jose Antonio, who was serving a sentence of 9 years and 8 months for stealing cars. She had brought their six-year-old daughter and a large pink suitcase, which is common for an overnight stay by family members in South American prison. Little did the guar如图，菱形ABCD的对角线AC长8，点P是对角线AC上的一个动点，点M、N分别是边AB、BC的中点，PM+PN的最小值是5，则菱形的边长等于____________。