import sys
k=int(1)
magic=1
s=0
a=list()
b=[0,0,0,0,0,0,0,0,0,0]
a=input().split()
for i in range(len(a)):
    a[i] = int(a[i])
b[a[len(a)-1]]=b[a[len(a)-1]]+1
for i in range(len(a)-2,-1,-1):
        for j in range((a[i]+1),10):
            if b[j]>0:
               s=s+(magic*b[j])/(b[a[i]]+1)
        b[a[i]]=b[a[i]]+1
        k=k+1
        magic=magic*k/(b[a[i]])
print ("%d" % (s))