import sys
input = lambda : sys.stdin.readline().rstrip()


sys.setrecursionlimit(2*10**5+10)
write = lambda x: sys.stdout.write(x+"\n")
debug = lambda x: sys.stderr.write(x+"\n")
writef = lambda x: print("{:.12f}".format(x))


k = int(input())
a = [0]*(k+1)
b = [0]*(k+1)
for i in range(k-1,-1,-1):
    aa = bb = 0
    for j in range(1,7):
        if i+j>k:
            aa += 1
        elif i+j<k:
            aa += a[i+j]
            bb += b[i+j]
    a[i] = aa/6
    b[i] = bb/6 + 1
ans = b[0] / (1-a[0])
print(ans)