#include<bits/stdc++.h>
using namespace std;
int n,k;
bitset<305>vis1[22][22][102],vis2[22][22][102];
string a,f1[22][22][102][305],f2[22][22][102][305];
void solve1(int m)
{
	f1[0][0][0][0]="";
	vis1[0][0][0][0]=1;
	for(int i=0;i<m;i++)
	{
		for(int j=0;j<=i;j++)
		{
			for(int k=0;k<=(i>>1)*(i+1>>1);k++)
			{
				for(int l=0;l<=300;l++)if(vis1[i][j][k][l])
				{
					if(a[i]=='?'||a[i]=='N')
					{
						if(!vis1[i+1][j+1][k][l])
						{
							vis1[i+1][j+1][k][l]=1;
							f1[i+1][j+1][k][l]=f1[i][j][k][l]+'N';
						}
					}
					if(a[i]=='?'||a[i]=='A')
					{
						if(!vis1[i+1][j][k+j][l])
						{
							vis1[i+1][j][k+j][l]=1;
							f1[i+1][j][k+j][l]=f1[i][j][k][l]+'A';
						}
					}
					if(a[i]=='?'||a[i]=='C')
					{
						if(!vis1[i+1][j][k][l+k])
						{
							vis1[i+1][j][k][l+k]=1;
							f1[i+1][j][k][l+k]=f1[i][j][k][l]+'C';
						}
					}
					if(a[i]!='N'&&a[i]!='A'&&a[i]!='C')
					{
						if(!vis1[i+1][j][k][l])
						{
							vis1[i+1][j][k][l]=1;
							f1[i+1][j][k][l]=f1[i][j][k][l]+(a[i]=='?'?'B':a[i]);
						}
					}
				}
			}
		}
	}
}
void solve2(int m)
{
	string a=::a;
	reverse(a.begin(),a.end());
	f2[0][0][0][0]="";
	vis2[0][0][0][0]=1;
	for(int i=0;i<m;i++)
	{
		for(int j=0;j<=i;j++)
		{
			for(int k=0;k<=(i>>1)*(i+1>>1);k++)
			{
				for(int l=0;l<=300;l++)if(vis2[i][j][k][l])
				{
					if(a[i]=='?'||a[i]=='C')
					{
						if(!vis2[i+1][j+1][k][l])
						{
							vis2[i+1][j+1][k][l]=1;
							f2[i+1][j+1][k][l]=f2[i][j][k][l]+'C';
						}
					}
					if(a[i]=='?'||a[i]=='A')
					{
						if(!vis2[i+1][j][k+j][l])
						{
							vis2[i+1][j][k+j][l]=1;
							f2[i+1][j][k+j][l]=f2[i][j][k][l]+'A';
						}
					}
					if(a[i]=='?'||a[i]=='N')
					{
						if(!vis2[i+1][j][k][l+k])
						{
							vis2[i+1][j][k][l+k]=1;
							f2[i+1][j][k][l+k]=f2[i][j][k][l]+'N';
						}
					}
					if(a[i]!='N'&&a[i]!='A'&&a[i]!='C')
					{
						if(!vis2[i+1][j][k][l])
						{
							vis2[i+1][j][k][l]=1;
							f2[i+1][j][k][l]=f2[i][j][k][l]+(a[i]=='?'?'B':a[i]);
						}
					}
				}
			}
		}
	}
}
int main()
{
	cin>>n>>k>>a;
	if(n<=20)
	{
		solve1(n);
		for(int i=0;i<=n;i++)for(int j=0;j<=n*n;j++)if(vis1[n][i][j][k])
		{
			cout<<f1[n][i][j][k]<<'\n';
			return 0;
		}
		cout<<"-1\n";
		return 0;
	}
	int m=n>>1;
	solve1(m);
	solve2(n-m);
	for(int i1=0;i1<=m;i1++)for(int j1=0;j1<=(m>>1)*(m+1>>1);j1++)
	{
		for(int i2=0;i2<=n-m;i2++)for(int j2=0;j2<=(n-m>>1)*(n-m+1>>1);j2++)
		{
			int sum=i1*j2+j1*i2;
			if(sum>k)continue;
			int l=k-sum;
			if(l>600)continue;
			for(int l1=max(l-300,0);l1<=min(l,300);l1++)if(vis1[m][i1][j1][l1])
			{
				int l2=l-l1;
				if(vis2[n-m][i2][j2][l2])
				{
					cout<<f1[m][i1][j1][l1];
					reverse(f2[n-m][i2][j2][l2].begin(),f2[n-m][i2][j2][l2].end());
					cout<<f2[n-m][i2][j2][l2]<<'\n';
					return 0;
				}
			}
		}
	}
	cout<<"-1\n";
}