1using System;
2
3public class ClosestPalindrome {
4    private static long MirrorPalindrome(string str) {
5        char[] chars = str.ToCharArray();
6        int n = chars.Length;
7        for (int i = 0; i < n / 2; i++) {
8            chars[n - 1 - i] = chars[i];
9        }
10        return long.Parse(new string(chars));
11    }
12
13    public static string Closest(string n) {
14        int len = n.Length;
15        long original = long.Parse(n);
16        long best = long.MaxValue;
17        string result = "";
18
19        // Generate basic, lower and higher mirroring
20        char[] lower = n.ToCharArray();
21        char[] higher = n.ToCharArray();
22
23        long mirrorValue = MirrorPalindrome(n);
24
25        // Compare different mirroring options
26        if (mirrorValue != original) best = mirrorValue;
27
28        lower[(len-1)/2]--;
29        long lowMirror = MirrorPalindrome(new string(lower));
30        if (Math.Abs(lowMirror - original) < Math.Abs(best - original) || (Math.Abs(lowMirror - original) == Math.Abs(best - original) && lowMirror < best)) {
31            best = lowMirror;
32        }
33
34        higher[(len-1)/2]++;
35        long highMirror = MirrorPalindrome(new string(higher));
36        if (Math.Abs(highMirror - original) < Math.Abs(best - original) || (Math.Abs(highMirror - original) == Math.Abs(best - original) && highMirror < best)) {
37            best = highMirror;
38        }
39
40        result = best.ToString();
41        return result;
42    }
43}