d = [0]
for i in range(1, 100):
    if i < 10:
        d.append(i)
    else:
        q, r = divmod(i, 10)
        d.append(q)
        d.append(r)
d.append(1)

n = int(input())
m = len(d)
for i in range(m - 1, -1, -1):
    d[i] *= n
for i in range(m - 1, 0, -1):
    if 10 <= d[i] < 100:
        q, r = divmod(d[i], 10)
        d[i] = r
        d[i - 1] += q
    else:
        q, r = divmod(d[i], 100)
        qq, r = divmod(r, 10)
        if i == 1:
            d[i] = r
            d[i - 1] += q * 10 + qq
        else:
            d[i] = r
            d[i - 1] += qq
            d[i - 2] += q

ans = str(d[0]) + '.' + ''.join(map(str, d[1:]))
print(ans)