#include <bits/stdc++.h>
int main(void) {
  int d[] = {-5, -1, 1, 5};
  int np, bp, tp, i, j, k, n;
  char s, t, b;
  for (; scanf("%d %c %c %c", &n, &s, &t, &b), n;) {
    double pr[2][25] = {};
    np = ((s - 'A') / 3 + 1) * 5 + (s - 'A') % 3 + 1;
    tp = ((t - 'A') / 3 + 1) * 5 + (t - 'A') % 3 + 1;
    bp = ((b - 'A') / 3 + 1) * 5 + (b - 'A') % 3 + 1;
    pr[n & 1][np] = 1.0;
    for (; n--;) {
      for (i = 1; i < 4; i++) {
        for (j = 1; j < 4; j++) {
          np = i * 5 + j;
          pr[n & 1][np] = 0.0;
          for (k = 0; k < 4; k++) {
            pr[n & 1][np] += pr[~n & 1][np + d[k]] / 4.0;
          }
        }
      }
      pr[n & 1][bp] = 0.0;
    }
    printf("%f\n", pr[0][tp]);
  }
  return 0;
}
