#include <bits/stdc++.h>
using namespace std;
const int N=1e4+10;
string tr[20],s;
int n,a[N],p;
bool Power(int n)
{
    if(n<=1)return 0;
    return (n&(n-1))==0;
}
int main()
{
	cin>>n>>s;
	for(int i=0;i<s.size();++i)
	{
		cout<<(s[i]=='0'?'B':'I');
		if(s[i]=='0')tr[0]+="B";
		if(s[i]=='1')tr[0]+="I";
		for(int j=0;j<=n;++j)
		{
			if(tr[j].size()>=2)
			{
				if(tr[j][0]==tr[j][1] && tr[j][0]!='F')tr[j+1]+=tr[j][0];
				else tr[j+1]+="F";
				cout<<tr[j+1][tr[j+1].size()-1];
				if(j+1==n)return 0;
				tr[j]="";
			}
			else
			{
				break;
			}
		}
	}
	return 0;
}

#include <iostream>
using namespace std;
int n;
char s[1<<20];
char type  [1<<20];
void dfs(int x){
	if(x>=(1<<n)){
		if(s[x]=='1'){
			type[x]='I';
		}
		else{
			type[x]='B';
		}
		cout<<type[x];
		return;
	}
	dfs(2*x);
	dfs(2*x+1);
	if(type[2*x]==type[2*x+1]){
		type[x]=type[2*x];
	}
	else{
		type[x]='F';
	}
	cout<<type[x];
}
int main(){
	cin>>n;
	for(int i=(1<<n);i<(1<<(n+1));i++){
		cin>>s[i];
	}
	dfs(1);
	return 0;
}