import math

def zeta(n):
    if n==2:
        return math.pi**2/6-1
    elif n==3:
        return 0.202056903159594
    else:
        ret=0
        for i in range(2,200):
            ret+=1/(i**n)
        return ret

n=int(input())
if n>=200:
    print(0)
else:
    ans=0
    for i in range(n,200):
        ans+=zeta(i)
    print(str(ans)[2:8])