from scipy.special import*
from math import*
ans = 0
x = int(input())
T = 1000000
for i in range(T):
    if x == 0 and i == 0 :
        ans = 1
    else :
        ans += sin(x + i) * sin(x + i) / (x + i) / (x+i)
ans += pi/2
S,C = sici((x + T-1)*2)
ans -= S
print(ans)