lines = sorted(int(x.strip()) for x in open("input.txt"))

prevs = [0, 0, 0, 1]
last = 0
for line in lines:
    mov = line - last
    last = line
    if mov > 0:
        prevs = prevs[mov:] + [0]*mov
        prevs[-1] = sum(prevs)

print(prevs[-1])