///////////////////////No.406 鴨等間隔の法則
    //入力文字読み取り
    process.stdin.resume();
    process.stdin.setEncoding('utf8');
    process.stdin.on('data', function (chunk) {


        //すべて受け取り改行で区切って格納
        var inputall = chunk.split("\n");

        //かもの総数
        var ducks = Number(inputall[0])

        //すべて受け取り空白で区切って格納
        //かもの座標配列
        var duckposition = inputall[1].split(" ").map(Number);

        //かもの座標配列を小さい順にソート
        duckposition.sort(function (a, b) {
            if (a < b) return -1;
            if (a > b) return 1;
            return 0;
        });

        var result = "YES";
        //同じのがあるか判定
        for (var i = 0; i < duckposition.length; i++) {
            for (var j = i + 1; j < duckposition.length-1; j++) {
                if (duckposition[i] == duckposition[j]) {
                    result = "NO";
                    break;
                }
            }
        }

        var difference = [];
        //座標が等間隔かを調べる
        for (var i = 0; i < duckposition.length-1; i++) {
            difference.push(duckposition[i + 1] - duckposition[i])
        }
        for (var i = 0; i < difference.length - 1; i++) {
            if (difference[i] == difference[i + 1]) {
                continue;
            } else {
                result = "NO";
                break;
            }
        }
        console.log(result);
    });