#include<bits/stdc++.h>
const int N=45,K=2505;
std::bitset<K> dp[N][N][N];//长度为i的前缀,前缀有j个N,后缀有k个C,前缀中的A总贡献为l是否能达到
int n,m;
std::string s,ans;
signed main(){
    std::ios::sync_with_stdio(0),std::cin.tie(0),std::cout.tie(0);
    std::cin>>n>>m>>s,s=' '+s;
    for(int k=0;k<=n;k++) dp[0][0][k][0]=1;
    for(int i=1;i<=n;i++) for(int j=0;j<=i;j++) for(int k=0;k<=n-i;k++){
        if(s[i]=='N'||s[i]=='?') if(j) dp[i][j][k]|=dp[i-1][j-1][k];
        if(s[i]=='C'||s[i]=='?') if(k+1<=n) dp[i][j][k]|=dp[i-1][j][k+1];
        if(s[i]=='A'||s[i]=='?') dp[i][j][k]|=dp[i-1][j][k]<<(j*k);
        if(s[i]!='N'&&s[i]!='A'&&s[i]!='C') dp[i][j][k]|=dp[i-1][j][k];
    }
    for(int i=0;i<=n;i++) if(dp[n][i][0][m]){
        int cn=i,cc=0,ck=m;
        for(int j=n;j>=1;j--){
            if((s[j]=='N'||s[j]=='?')&&cn&&dp[j-1][cn-1][cc][ck]) ans+='N',cn--;
            else if((s[j]=='C'||s[j]=='?')&&cc+1<=n&&dp[j-1][cn][cc+1][ck]) ans+='C',cc++;
            else if((s[j]=='A'||s[j]=='?')&&ck>=cn*cc&&dp[j-1][cn][cc][ck-cn*cc]) ans+='A',ck-=cn*cc;
            else if(s[j]=='?') ans+='G';
            else ans+=s[j];
        }
        std::reverse(ans.begin(),ans.end());
        std::cout<<ans;
        return 0;
    }
    std::cout<<-1;
    return 0;
}