n=int(input())
l,r=map(int,input().split())

dp=[[0 for i in range(6*n+1)]  for j in range(n+1)] 

dp[1][1:7]=[1 for i in range(6)]
for i in range(1,n):
    for j in range(1,6*(i+1)):
        s=0
        for k in range(1,7):
            if j-k>0:
                s+=dp[i][j-k]
            dp[i+1][j]=s

a=sum([dp[n][i] for i in range(l,r+1)])
print(a/6**n)