Help me WA4?
#include <iostream>
#include <string>
#include <string.h>
#include <algorithm>
using namespace std;
string S, ss, s;
int k, l, r, mid;
int main(){
    cin >> S;
    int n = S.size();
    if(n == 1){
        cout << S;
        return 0;
    }
    for (int i = n - 1; i >= 0; i --){
        k = n - i;
        if(i - k >= 0){
            ss = S.substr(i, k);
            s = S.substr(i - k, k);
            reverse(s.begin(), s.end());
            //cout << ss << ' ' << s << endl;
            if(ss == s){
                l = i - k;
                mid = i;
                r = i + k;
                continue;
            }
        }
        k --;
        if(i - k >= 0){
            ss = S.substr(i + 1, k);
            s = S.substr(i - k, k);
            reverse(s.begin(), s.end());
            //cout << ss << ' ' << s << endl;
            if(ss == s){
                l = i - k;
                mid = i;
                r = i + k;
            }
        }
    }
    //cout << l << ' ' << r << endl;
    if(!l && !r || (l == 0 && r == n - 1)){
        s = S.substr(0, n - 1);
        cout << S;
        reverse(s.begin(), s.end());
        cout << s;
    }
    else{
        s = S.substr(0, l);
        reverse(s.begin(), s.end());
        cout << S << s;
    }
    return 0;
}