How can I set textures the user chooses with website id?

Players in game will be setting decal id's with the websites url decal id. Which is not the same as the asset id for some reason. When setting the decal to the numbers the player put it will become grey because it can not load. How can I make this work?

local PreDecal = 'http://roblox.com/asset/?id='
local TexturePlayerPicked = 475313577

local Button = Instance.new('ImageButton',Frame)
Button.Image = PreDecal..TexturePlayerPicked