import sys n= int(input()) y = 0 lst = [] if n == 1: y = 0 print(y) elif 2<= n <=3: y = 1 print(y) else: a1,a2,a3 = 0,1,1 for i in range(4,n+1): a_nest = a1 + 2*a2 +a3 a1,a2,a3 = a2,a3,a_nest print(a_nest)