#!/usr/bin/env python3 from sys import argv i = {int(x.strip()) for x in open(argv[1])} i.add(0) i.add(max(i)+3) s = sorted(list(i)) di = [0]*3 for x in range(len(s)-1): d = s[x+1] - s[x] di[d-1] += 1 print(di[0]*di[2]) ch = {} def f(x): if x not in i: return 0 if x in ch: return ch[x] c = f(x+1) + f(x+2) + f(x+3) if not c: c += 1 ch[x] = c return c print(f(0))