As shown in the figure, in the isosceles triangle ABC, point P is a moving point on the bottom edge AC, and m and N are the midpoint of AB and BC respectively. If the minimum value of PM + PN is 2, then the perimeter of △ ABC is___ .

As shown in the figure, in the isosceles triangle ABC, point P is a moving point on the bottom edge AC, and m and N are the midpoint of AB and BC respectively. If the minimum value of PM + PN is 2, then the perimeter of △ ABC is___ .

Make the symmetry point m'of m point about AC, connect M'n, the intersection point with AC is the position of P point, ∵ m, n are the midpoint of AB and BC respectively, ∵ Mn is the median line of △ ABC, ∵ Mn ∥ AC, Mn = 12ac, ∵ PM ′ PN = km ′ km = 1,