long long Convert(long long& num)
    {
        string s = to_string(num);
        int n = s.length();
        int l = (n-1) / 2;
        int r = n / 2;
        while(l >= 0) s[r++] = s[l--];
        return stoll(s);
    }

long long UpPal(long long num)
    {
        long long left = 0;
        long long right = num;
        long long ans = INT_MIN;
        
        while(left <= right)
        {
            long long mid = (right + left)/2;
            long long palin = Convert(mid);
            if(palin < num) 
            {
                ans = palin;
                left = mid + 1;
            }
            else
            {
                right = mid - 1;
            }
        }
        
        return ans;
    }
    
    long long DownPal(long long num)
    {
        long long left = num;
        long long right = 1e18;
        long long ans = INT_MIN;
        
        while(left <= right) {
            long long mid = (right + left) / 2;
            long long palin = Convert(mid);
            if(palin > num)
            {
                ans = palin;
                right = mid - 1;
            }
            else 
            {
                left = mid + 1;
            }
        }
        
        return ans;
    }

class Solution {
public:
    string nearestPalindromic(string n) {
        if(n.length()==1)
            return to_string(stoi(n)-1);
        
        int d = n.length();
        vector<long> candidates;
        candidates.push_back(pow(10,d-1)-1);
        candidates.push_back(pow(10,d)+1);

        int mid = (d+1)/2;
        long prefix = stol(n.substr(0,mid));
        vector<long> v = {prefix,prefix+1, prefix-1};
        for(long i : v)
        {
            string postfix = to_string(i);
            if(d%2!=0)
                postfix.pop_back();
            reverse(postfix.begin(), postfix.end());
            string c = to_string(i)+postfix;
            candidates.push_back(stol(c));
        }
        long mindiff = LONG_MAX;
        long result;
        long num = stol(n);
        for(int i=0;i<5;i++)
        {
            if(candidates[i]!=num && abs(candidates[i]-num)<mindiff)
            {
                mindiff = abs(candidates[i]-num);
                result = candidates[i];
            }
            else if(abs(candidates[i]-num)==mindiff)
                result = min(result, candidates[i]);
        }
        return to_string(result);
    }
};