#include <iostream>
#include <string>
 
using namespace std;
 
int main() {
	// your code goes here
	int n;
	string s, t;
	string m;
	bool inicio=true;
	bool dif=false;
	char ans;
	cin>>n;
	cin>>s;
	int w=s.size();
 
	for (int q=1;q<n;q++)
	{cin>>t;
		for (long long int i=0;i<=w;i++)
	{
		if(s[i]=='?')
		 s[i]=t[i];
		else if (t[i]!='?'&&s[i]!=t[i])
		 s[i]='!';
}
		}
	for(int i=0;i<w;i++)
	{
		if(s[i]=='?') s[i]='y';
else if(s[i]=='!') s[i]='?';
	}
	cout<<s<<endl;
	return 0;
}

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1
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