#include<iostream>
#include<cmath>

#define WIDTH 3
#define HEIGHT 3
#define ERORR -1

using namespace std;

int main()
{
	int n, ctl, map[2][HEIGHT+2][WIDTH+2], sx, sy, gx, gy, xx, yy, tx, ty;
	int dx[] = {0, 0, -1, 1}, dy[] = {-1, 1, 0, 0};
	char s, t, b;
	while(cin >> n, n) {
		ctl = 0;
		cin >> s >> t >> b;
		for(int i=0; i < HEIGHT+2; i++)
			for(int j=0; j < WIDTH+2; j++) {
				for(int k=0; k < 2; k++) {
					if(i == 0 || i == HEIGHT+1 || j == 0 || j == WIDTH+1)
						map[k][i][j] = ERORR;
					else
						map[k][i][j] = 0;
				}
			}
		sx = (s-'A') % WIDTH + 1; sy = (s-'A') / WIDTH + 1;
		gx = (t-'A') % WIDTH + 1; gy = (t-'A') / WIDTH + 1;
		xx = (b-'A') % WIDTH + 1; yy = (b-'A') / WIDTH + 1;
		map[0][yy][xx] = map[1][yy][xx] = ERORR;
		map[ctl][sy][sx] = 1;
		int sum = 1 << (2 * n);
		while(n--) {
			for(int i=1; i <= HEIGHT; i++) {
				for(int j=1; j <= WIDTH; j++) {
					if(map[(ctl+1)%2][i][j] == ERORR) continue;
					map[(ctl+1)%2][i][j] = 0;
					for(int d=0; d < 4; d++) {
						tx = j + dx[d]; ty = i + dy[d];
						if(map[ctl][ty][tx] == ERORR) { tx = j; ty = i; }
						map[(ctl+1)%2][i][j] += map[ctl][ty][tx];
					}
				}
			}
			ctl = (ctl+1) % 2;
		}
		printf("%.8f\n", (float)(map[ctl][gy][gx])/sum);
		
	}
	return 0;
}