#include <bits/stdc++.h>
using namespace std;

int n,a[35],pos,cnt;
char s[1000005];

int main () {
	scanf("%d",&n);
	for (int i = 1;i <= n;i++) scanf("%1d",&a[i]);
	for (int i = n;i >= 1;i--) {
		if (a[i] == 1) cnt++;
		if (a[i] == 0 && cnt != 0) {
			for (int j = 1;j <= i + cnt;j++) s[++pos] = 'A';
			for (int j = 1;j <= i;j++) s[++pos] = 'B';
			cnt = 0;
		}
	}
	if (cnt != 0) for (int i = 1;i <= cnt;i++) s[++pos] = 'A';
	printf("%d\n",pos);
	for (int i = 1;i <= pos;i++) printf("%c",s[i]);
	return 0;
}