#include<bits/stdc++.h>
using namespace std;
int h[14]={1,2,4,8,16,32,64,128,256,512,1024,2048};
int arr[100005];
int main(){
    int f;
    cin>>f;
    for(int i=0;i<=h[f];i++){
        char a;
        cin>>a;
        arr[i]=a-'0';
        if(arr[i]==0) cout<<"B";
        else if(arr[i]==1) cout<<"I";
        else cout<<"F";
        for(int j=1;j<=11;j++){
            if(i%h[j]==0){
                if(arr[i]!=arr[i-h[j-1]]) arr[i]=2;
                if(arr[i]==0) cout<<"B";
            else if(arr[i]==1) cout<<"I";
            else cout<<"F";
            }
        }
    }
}