N=10
ans=0
for i in range(1,N+1):
  for j in range(i+2,N+1):
    for k in range(j+2,N+1): ans+=1
print(ans)

N=90
# ~ ans=0
# ~ for i in range(1,N+1):
  # ~ for j in range(i+2,N+1):
    # ~ for k in range(j+2,N+1): 
      # ~ for l in range(k+2,N+1):
        # ~ for m in range(l+2,N+1): ans+=1
# ~ print(ans)


# ~ import math as MAT
# ~ comb=lambda n,k: MAT.factorial(n)//MAT.factorial(k)//MAT.factorial(n-k)

# ~ print(ans/comb(90,5))

import random as RN


def nincsszomszedos():
  prev=-1
  for v in sorted(RN.sample(range(1,91),5)):
    if v-prev==1: return False
    prev=v
  return True

N=10000000
K=0
for _ in range(N):
  K+=nincsszomszedos()
print(K/N)