from __future__ import division
def FuncSum(n):
s=1;f=1
for i in range(1,n+1):
f*=i
s+=1/f;
return s
if __name__=="__main__":
n=int(input("please input number n:"))
if 1 print("s=%f"%FuncSum(n))
else:
raise ValueError("n must big than 1 and less or equal 20")
