#include<bits/stdc++.h>usingnamespacestd;stringrichieRich(string s,int n,int k){int lives=k;   vector<bool>mod(n,false);     stringtemp(s);for (int i=0;i<n/2;i++)    {if (temp[i]!=temp[n-i-1]) {mod[i]=true;lives--;}if (temp[i]<temp[n-i-1]) temp[i]=temp[n-i-1];elseif (temp[i]>temp[n-i-1]) temp[n-i-1]=temp[i];if (lives<0)return"-1";          }int j=0;while ((lives>0)&&(j<n/2))   {if (temp[j]!='9'){if (mod[j]) lives++;if (lives>1) {temp[j]='9';temp[n-j-1]='9'; lives-=2;}      }             j++;           }if (n%2==1) {if (lives>0) temp[n/2]='9';}return temp;}intmain() {int n;    cin >> n;int k;    cin >> k;    string s;    cin >> s;    string result =richieRich(s, n, k);    cout << result << endl;return0;}