static bool KiemTraSoHoanHao(int N)
for(int i=1; i<=N/2; i++)
static bool KiemTraSoNguyenTo(int N)
for(int i=2; i<=N/2; i++)
public static void Main()
Console.WriteLine("Nhap N: ");
int N = int.Parse(Console.ReadLine());
if(KiemTraSoNguyenTo(i)) Sum = Sum +i;