D = "0.1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980818283848586878889909192939495969798991"

L = 190
N = int(input())
DL = []
for d in reversed(D[2:]):
    DL.append(int(d))
DL += [0]
A = [0] * (L+1)
for i in range(L):
    A[i] += N * DL[i]
    A[i+1] += A[i] // 10
    A[i] %= 10
A = [str(s) for s in A]
A = A[::-1]
ans = A[0] + "."
ans += "".join(A[1:])
print(ans)