def func(a,isEnd=0):
    sum=1.0
    if isEnd==1:
        i=1
        t=1
        while t>10**-4:
            t=1
            for j in range(1,i+1):
                t=t/j
            sum=sum+t
            i=i+1
        return sum
    else:         
        for i in range(1,a):
                t=1.0
                for j in range(1,i+1):
                    t=t/j
                sum=sum+t
    return sum
if __name__=="__main__":
    print(func(50))
    print(func(1,1,))
   

2.7182818284590455
2.71827876984127