Insert With Parameters (SQL Server)

Hello, this is my code:


 SqlCommand cmd = new SqlCommand("INSERT INTO Users (Username,Password) " +
"VALUES ('@username','@password' ", new SqlConnection(my_ConnectionString));

cmd.Parameters.Add("@username", SqlDbType.NVarChar, 50).Value = txtUsername.Text;
cmd.Parameters.Add("@password", SqlDbType.NVarChar, 50).Value = txtPassword.Text

cmd.Connection.Open();
cmd.ExecuteNonQuery();
cmd.Connection.Close(); 
But in the database, the row inserted is exactly this:

"@username" "@password"

I mean, the parameters are not inserted :S

Please, tell me the error in the code...
Thank you so much,

Carlos.