[Лоэнрон]

function getNum(arr, a){
	arr.sort();
	for(let i = 0; i < arr.length; i++){
		if(arr[i] > a){
			if(i == 0) return `${arr[i]}`;
			if( (arr[i] - a) > (arr[i-1] - a) ){
				return `${arr[i-1]},${arr[i]}`;
			} else {
				return `${arr[i-1]},${arr[i-2]}`;
			}
		} else if (i == arr.length - 1){
			return `${arr[i]}`;
		}
	}
}

let arr = [99,56,87,78,66,55];

console.log(getNum(arr, 88)); // 87,99
console.log(getNum(arr, 100)); // 99
console.log(getNum(arr, 10)); // 55