以下C#程序的输出结果是（ ）。

using System;

namespace HoverTreeTikuConsole
{
class Program
{
static void Main(string[] args)
{
MyStruct s1 = new MyStruct(1, 2);
s1.x = 2;
s1.Sum();
Console.ReadLine();
}
}

/// <summary>
/// http://hovertree.com/h/bjaf/g8bsql7s.htm
/// </summary>
struct MyStruct
{
public int x;
public int y;
public MyStruct(int i, int j)
{
x = i;
y = j;
}
public void Sum()
{
int sum = x + y;
Console.WriteLine("the sum is {0}", sum);
}
}