#include <bits/stdc++.h>
double f[17][3][3];
int mv[4][2] = {{-1, 0}, {0, 1}, {1, 0}, {0, -1}};
int main() {
  int n, s, t, b, i, j, r, c, r2, c2;
  char t1[5], t2[5], t3[5];
  while (scanf("%d", &n) && n) {
    scanf("%s%s%s", t1, t2, t3), s = *t1 - 'A', t = *t2 - 'A', b = *t3 - 'A';
    memset(f, 0, sizeof(f)), f[0][s / 3][s % 3] = 1.0;
    for (j = 1; j <= n; j++) {
      for (r = 0; r < 3; r++)
        for (c = 0; c < 3; c++) {
          for (i = 0; i < 4; i++) {
            r2 = r + mv[i][0], c2 = c + mv[i][1];
            if (r2 < 0 || r2 >= 3 || c2 < 0 || c2 >= 3 || 3 * r + c == b)
              f[j][r][c] += f[j - 1][r][c] / 4.0;
            else
              f[j][r2][c2] += f[j - 1][r][c] / 4.0;
          }
        }
    }
    printf("%.8lf\n", f[n][t / 3][t % 3]);
  }
  return 0;
}
