#include<bits/stdc++.h>
using namespace std;
int n,m;
char str[50];
bitset<2501>f[45][45][45];
int main(){
   scanf("%d%d%s",&n,&m,str+1);
   for(int i=0;i<=n;i++)f[0][0][i].set(0);
   for(int i=0;i<n;i++){
      for(int j=0;j<=n;j++)for(int k=0;j+k<=n;k++){
         if(str[i+1]=='N'||str[i+1]=='?')f[i+1][j+1][k]|=f[i][j][k];
         if(str[i+1]=='C'||str[i+1]=='?')f[i+1][j][k-1]|=f[i][j][k];
         if(str[i+1]=='A'||str[i+1]=='?')f[i+1][j][k]|=f[i][j][k]<<j*k; 
         if(str[i+1]=='?'||(str[i+1]!='A'&&str[i+1]!='C'&&str[i+1]!='N'))f[i+1][j][k]|=f[i][j][k];
      }
   }
   int x=-1,y=0;
   for(int i=0;i<=n;i++)if(f[n][i][0][m]){x=i;break;}
   if(x==-1)return puts("-1"),0;
   auto findst=[](int i,int x,int y,int c,int&rx,int&ry,int&rc){
      for(int j=0;j<=n;j++)for(int k=0;j+k<=n;k++){
         if((str[i+1]=='N'||str[i+1]=='?')&&j+1==x&&k==y&&f[i][j][k][c])return rx=j,ry=k,rc=c,'N';
         if((str[i+1]=='C'||str[i+1]=='?')&&j==x&&k-1==y&&f[i][j][k][c])return rx=j,ry=k,rc=c,'C';
         if((str[i+1]=='A'||str[i+1]=='?')&&j==x&&k==y&&c>=j*k&&f[i][j][k][c-j*k])return rx=j,ry=k,rc=c-j*k,'A'; 
         if((str[i+1]=='?'||(str[i+1]!='A'&&str[i+1]!='C'&&str[i+1]!='N'))&&j==x&&k==y&&f[i][j][k][c])return rx=j,ry=k,rc=c,str[i+1]=='?'?'O':str[i+1];
      }
   };
   for(int i=n;i>=1;i--){
      str[i]=findst(i-1,x,y,m,x,y,m);
   }
   printf("%s",str+1);
   return 0;
}