#include <bits/stdc++.h>
using namespace std;
int patterns[2][10];
int s, t, b;
void getMovablePoints(int* ret, int s) {
  ret[0] = s - 3;
  ret[1] = s + 1;
  ret[2] = s + 3;
  ret[3] = s - 1;
  for (int i = 0; i < 4; i++) {
    if (ret[i] < 0 || 8 < ret[i] || ret[i] == b) ret[i] = s;
  }
}
int main() {
  int n;
  while (cin >> n, n) {
    char _s, _t, _b;
    cin >> _s >> _t >> _b;
    s = _s - 'A';
    t = _t - 'A';
    b = _b - 'A';
    for (int i = 0; i < 9; i++) {
      patterns[0][i] = patterns[1][i] = 0;
    }
    patterns[0][s] = 1;
    int *pattern, *nextPattern;
    for (int i = 0; i < n; i++) {
      pattern = patterns[i % 2];
      nextPattern = patterns[(i + 1) % 2];
      for (int j = 0; j < 9; j++) {
        nextPattern[j] = 0;
      }
      for (int j = 0; j < 9; j++) {
        int movablePoints[4];
        getMovablePoints(movablePoints, j);
        for (int k = 0; k < 4; k++) {
          nextPattern[movablePoints[k]] += pattern[j];
        }
      }
    }
    int sum = 0;
    for (int i = 0; i < 9; i++) {
      sum += nextPattern[i];
    }
    printf("%.8f\n", (double)nextPattern[t] / sum);
  }
  return 0;
}
