#include<cstdio>
#include<cstring>
using namespace std;
const int N=10;
char fbi[1<<(N+2)],inc[1<<(N+1)];
int n,len;
void printt(int u){
	if(u>=(1<<(n+1)))return;
	printt(u<<1),printt(u<<1|1);
	putchar(fbi[u]);
}
int main(){
	scanf("%d%s",&n,inc);len=strlen(inc);
	for(int i=0;i<len;++i)fbi[(1<<n)+i]=(inc[i]=='1'?'I':'B');
	for(int i=(1<<n)-1;i;--i)
		fbi[i]=(fbi[i<<1]==fbi[i<<1|1]?fbi[i<<1]:'F');
	printt(1);
	return 0;
}