import sys
input=sys.stdin.readline
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))
mod=10**9+7

def main():
    p=float(input())
    if p==0:
        print(0)
    else:
        print(1/(1-p)-1)


main()