#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;
}