You are doing
Console.WriteLine("tot=" + res);
I think the res in the above statement should be tot
before
int res = x * y;
There is a lot wrong with your code,
Console.Write("x=");
Console.Write("y=");
int x = int.Parse(Console.ReadLine());
int y = int.Parse(Console.ReadLine());
should be
Console.Write("x=");
int x = int.Parse(Console.ReadLine());
Console.Write("y=");
int y = int.Parse(Console.ReadLine());