#!/bin/python

with open("input", 'r') as input:
    adapters = [int(i.strip()) for i in input]
    adapters.sort()
    adapters.insert(0, 0)
    adapters.append(adapters[-1]+3)
    print(adapters)
    i = 0
    ones = 0
    threes = 0
    while i < len(adapters)-1:
        if adapters[i+1] - adapters[i] == 1:
            ones += 1
        elif adapters[i+1] - adapters[i] == 3:
            threes += 1

        i += 1
    

    print(ones * threes)