problem in delegate?

namespace review_of_c
{
class Program
{

public delegate int m(int x, int y);

static void Main(string[] args)
{
m res= new m(sum);
res += new m(mult);
int d=res(5,6);
Console.WriteLine(d);

}
public static int sum(int x, int y)
{
int z = x + y;
return z;

}
public static int mult(int x, int y)
{
int z = x * y;
return z;

}

}

this code give me one result for one fuction (mult), why? i want to obtain the both functions result (mult)and(sum) , plz help me.