C#自动编号，要求编号连续不间断

public static int getcode()
{
int[] num = { 0, 1, 2, 4, 5 };
List test = new List(num);
int i = 1;
for (; i < test.Count; i++)
{
if (test[i - 1] + 1 != test[i])
{
break;
}
}
return test[i - 1] + 1;
}