import sys
stdin = sys.stdin
sys.setrecursionlimit(10**6)
ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
nn = lambda: list(stdin.readline().split())
ns = lambda: stdin.readline().rstrip()

p = float(input())
pp = 1
ans = 0
for i in range(1,10000):
    pp *= p
    ans += i*(1-pp)

print(ans)