list{1,4,7,6}

getNearestTop(int input){
        return list.OrderBy(i => i)
                   .First();

}

getNearestBottom(int input){
    return list.OrderBy(i => i)
               .Last();
}

getNearestBottom(5) should return 4
getNearestTop(5)    should return 6
getNearestBottom(4) should return 1