Hangzhou Electric 1001 Sum problem

First look at the topic

This problem, according to the meaning of the title, I understand, should be input, each group input line, and then the corresponding output, more than one blank line between the output, but the problem is how to know that he has entered the completed, the following should show the output. Misunderstood by the problem input and output case. It was then replaced by a line of output, followed by the output of the line, and then the input, output, alternating.

#include <iostream>

using namespace Std;

int Sum (int);

int main ()
{
int Inputa;

while (Cin>>inputa)
{
Cout<<sum (Inputa) <<endl<<endl;
}

return 0;
}

int Sum (int n)
{
if (n==1) return 1;
else return n+sum (n-1);
}

Hangzhou Electric 1001 Sum problem