13．在直三棱柱ABC−A1B1C1ABC-A_{1}B_{1}C_{1}ABC−A1B1C1中AB=BC=2AB=BC=\sqrt{2}AB=BC=2，BB1=2BB_{1}=2BB1=2，∠ABC=90∘\angle ABC=90\circ∠ABC=90∘，EEE、FFF分别为AA1AA_{1}AA1、C1B1C_{1}B_{1}C1B1的中点，沿棱柱的表面从EEE到FFF两点的最短路径的长度为((( )))
