#include<bits/stdc++.h>
#define ll long long
#define N 53
#define K 2550
using namespace std;
int read(){
    int x=0,f=1;char ch=getchar();
    while(ch<'0' && ch>'9')f=(ch=='-'?-1:f),ch=getchar();
    while(ch>='0' && ch<='9')x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
    return x*f;
}
void write(int x){
    if(x<0)x=-x,putchar('-');
    if(x/10)write(x/10);
    putchar(x%10+'0');
}
char s[N],res[N];
vector f(N,vector(N,vector(N,bitset<K>{})));
int main(){
    #ifdef EAST_CLOUD
    freopen("a.in","r",stdin);
    freopen("a.out","w",stdout);
    #endif
    int n=read(),m=read();scanf("%s",s+1);
    for(int i=0;i<=n;i++){
        f[0][0][i][0]=1;
    }
    for(int i=1;i<=n;i++){
        if(s[i]=='?' || s[i]=='N'){
            for(int j=1;j<=i;j++){
                for(int k=0;k<=n-i;k++){
                    f[i][j][k]|=f[i-1][j-1][k];
                }
            }
        }
        if(s[i]=='?' || s[i]=='A'){
            for(int j=0;j<=i;j++){
                for(int k=0;k<=n-i;k++){
                    f[i][j][k]|=f[i-1][j][k]<<(j*k);
                }
            }
        }
        if(s[i]=='?' || s[i]=='C'){
            for(int j=0;j<=i;j++){
                for(int k=0;k<=n-i;k++){
                    f[i][j][k]|=f[i-1][j][k+1];
                }
            }
        }
        if(s[i]=='?' || (s[i]!='C' && s[i]!='A' && s[i]!='N')){
            for(int j=0;j<=i;j++){
                for(int k=0;k<=n-i;k++){
                    f[i][j][k]|=f[i-1][j][k];
                }
            }
        }
    }
    int Nc=0,Cc=0,Kc=0,flag=0;
    for(int i=0;i<=n;i++){
        if(f[n][i][0][m]){
            Nc=i;Kc=m;flag=1;break;
        }
    }
    if(!flag){cout<<-1;return 0;}
    for(int i=n;i>=1;i--){
        if(s[i]=='?' || s[i]=='N'){
            if(Nc-1>=0 && f[i-1][Nc-1][Cc][Kc]){
                Nc--;res[i]='N';continue;
            }
        }
        if(s[i]=='?' || s[i]=='C'){
            if(Cc+1<N && f[i-1][Nc][Cc+1][Kc]){
                Cc++;res[i]='C';continue;
            }
        }
        if(s[i]=='?' || s[i]=='A'){
            if(Kc-Nc*Cc>=0 && f[i-1][Nc][Cc][Kc-Nc*Cc]){
                Kc-=Nc*Cc;res[i]='A';continue;
            }
        }
        if((s[i]!='C' && s[i]!='A' && s[i]!='N')){
            if(f[i-1][Nc][Cc][Kc]){
                res[i]='B';continue;
            }
        }
    }
    for(int i=1;i<=n;i++)cout<<res[i];
    return 0;
}