#include<bits/stdc++.h>
#define rep(i,a,b) for (int i=(a);i<=(b);i++)
#define drep(i,a,b) for (int i=(a);i>=(b);i--)
typedef long long ll;
using namespace std;

#define fir first
#define sec second

bitset<2501> f[21][101],g[21][101];
vector<int> vf[21][101],vg[21][101];

int main()
{
	ios::sync_with_stdio(false); cin.tie(0);
	
	int n,k; 
	string s;
	cin>>n>>k>>s;
	map<array<int,3>,string> mp1,mp2;
	mp1[{0,0,0}]=mp2[{0,0,0}]="";
	
	int m=n/2;
	rep(i,0,m-1)
	{
		char ch=s[i];
		map<array<int,3>,string> nmp;
		auto test=[&](const array<int,3> &f,const string &t,char c)
		{
			array<int,3> g=f;
			if (c=='N') g[0]++;
			if (c=='A')	g[1]+=f[0];
			if (c=='C') g[2]+=f[1];
			if (g[2]>k) return;
			nmp[g]=t+c;
		};
		for (auto it:mp1)
		{
			if (ch!='?') test(it.fir,it.sec,ch);
			else
			{
				test(it.fir,it.sec,'N');
				test(it.fir,it.sec,'A');
				test(it.fir,it.sec,'C');
				test(it.fir,it.sec,'D');
			}
		} 
		swap(mp1,nmp);
	}
	drep(i,n-1,m)
	{
		char ch=s[i];
		map<array<int,3>,string> nmp;
		auto test=[&](const array<int,3> &f,const string &t,char c)
		{
			array<int,3> g=f;
			if (c=='C') g[0]++;
			if (c=='A')	g[1]+=f[0];
			if (c=='N') g[2]+=f[1];
			if (g[2]>k) return;
			nmp[g]=t+c;
		};
		for (auto it:mp2)
		{
			if (ch!='?') test(it.fir,it.sec,ch);
			else
			{
				test(it.fir,it.sec,'N');
				test(it.fir,it.sec,'A');
				test(it.fir,it.sec,'C');
				test(it.fir,it.sec,'D');
			}
		} 
		swap(mp2,nmp);
	}
//	printf("search done\n");
//	printf("%d\n",clock());
	
	vector<array<int,3> > v1,v2;
	for (auto it:mp1)
	{
		auto t=it.fir;
		vf[t[0]][t[1]].push_back(t[2]);
		f[t[0]][t[1]][t[2]]=1; 
	}
	for (auto it:mp2)
	{
		auto t=it.fir;
		vg[t[0]][t[1]].push_back(t[2]);
		g[t[0]][t[1]][k-t[2]]=1;
	}
	
	rep(x,0,20) rep(y,0,100) if (vf[x][y].size())
	{
		rep(a,0,20) rep(b,0,100) if (vg[a][b].size())
		{
			int v=x*b+y*a;
			if (v>k) continue;
//			printf("chk x %d y %d a %d b %d\n",x,y,a,b);
//			for (auto z:vf[x][y]) printf("z %d\n",z);
//			for (auto c:vg[a][b]) printf("c %d\n",c);
			if (((f[x][y]<<v)&g[a][b]).count())
			{
				for (auto z:vf[x][y])
				{
					if (mp2.count({a,b,k-v-z}))
					{
						auto s=mp1[{x,y,z}];
						auto t=mp2[{a,b,k-v-z}];
						reverse(t.begin(),t.end());
						cout<<s<<t<<"\n";
						return 0;
					}
				}	
				assert(0);
			} 
		}
	}
	
	printf("-1\n");
	
	return 0;
}