import sys def count(a): return a // 3, a // 3 + a % 3 for line in sys.stdin: a = int(line.strip()) if a == 0: break count1 = 0 a1, a2 = count(a) while a2 >= 2 or a1 != 0: if a1 == 0 and a2 == 2: count1 += 1 break count1 += a1 a1, a2 = count(a2) print(count1)