import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int K = sc.nextInt();
    // dp[i][j][k]は(i+1)個のサイコロでK=jの場合に、太郎-二郎=k-50となる確率
    double[][][] dp = new double[10][11][101];
    for(int i = 1; i <= 6; i++) {
      for(int j = 1; j <= 6; j++) {
        dp[0][0][i - j + 50] += (double)1 / (double)36;
      }
    }
    for(int i = 4; i <= 6; i++) {
      for(int j = 1; j <= 6; j++) {
        dp[0][1][i - j + 50] += (double)1 / (double)18;
      }
    }
    for(int i = 1; i < 10; i++) {
      for(int k = 0; k < 101; k++) {
        for(int m = 1; m <= 6; m++) {
          for(int n = 1; n <= 6; n++) {
            if(k - m + n >= 0 && k - m + n < 101) dp[i][0][k] += (double)1 / (double)36 * dp[i - 1][0][k - m + n];
          }
        }
      }
      for(int j = 1; j <= i + 1; j++) {
        for(int k = 0; k < 101; k++) {
          for(int m = 4; m <= 6; m++) {
            for(int n = 1; n <= 6; n++) {
              if(k - m + n >= 0 && k - m + n < 101) dp[i][j][k] += (double)1 / (double)18 * dp[i - 1][j - 1][k - m + n];
            }
          }
        }
      }
    }
    double ans = 0;
    for(int k = 51; k < 101; k++) {
      ans += dp[N - 1][K][k];
    }
    System.out.println(ans);
  }
}