import collections if __name__ == '__main__': with open("input.txt") as f: raw = [0] for i in f.read().splitlines(): raw.append(int(i)) raw = sorted(raw) raw.append(max(raw) + 3) diffs = [] for i in range(1, len(raw)): diffs.append(raw[i] - raw[i - 1]) diff_counter = collections.Counter(diffs) print(diff_counter[1] * diff_counter[3]) ways = [1] + [0]*raw[-1] for i in raw[1:]: ways[i] = ways[i-1] + ways[i-2] + ways[i-3] print(ways[-1])