#include <bits/stdc++.h>
using namespace std;
const int N=200005;
int c[N];
int s,n,m,x,p;
string a,b;
int main(){
	cin>>n>>m;
	cin>>a>>b;
	for(int i=0;i<a.size();i++){
		if(a[i]=='#')s++;
	}
	s=m-s;
	x=s/26+1;
	for(int i=0;i<a.size();i++){
		if(a[i]!='#')continue;
		if(x){
			a[i]='a';
			x--;
		}
		else{
			p++;
			if(p>=26)p=0;
			//cout<<p<<" ";
			a[i]='a'+p;
		}
	}
	//cout<<"\n";
	cout<<a;
	return 0;
}