Hi! I want to input IdContact as routeValue in @html.BeginForm...how I do this ?Thanks

@Html.BeginForm("ShowDetails", "Home", new { id="opt1"})
@*@Html.DropDownListFor(m => m.FirstName, new SelectList(ViewBag.ListContact));*@
<div>
<select id="Select1">
    @foreach(var c in Model)
    { 
    <option value="@c.IdContact" id="opt1">
        @c.FirstName   @c.LastName
    </option>
        
    }
</select>
    <input type="submit" onsubmit="" />
    </div>