import sys
input = sys.stdin.readline
def zeta(n):
    res = 0
    for i in range(1, 1000):
        if i**n > 10**20:
            break
        res += 10**6/i**n
    return res
ans = 0
x = int(input())
for i in range(x, x+300):
    ans += zeta(i)
ans = str(ans).split(".")[0]
print(ans[3:])