#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (int i = (int)a; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MOD 1000000007
#define INF 1000000000
#define PI 3.14159265359
#define EPS 1e-12

int main(void) {
  int n, k;
  cin >> n >> k;

  int tot = 0, win = 0;
  REP(j, 1000000) {
    int a = 0, b = 0;
    REP(i, n) a += rand() % 6 + 1;
    REP(i, k) b += rand() % 3 + 4;
    REP(i, n - k) b += rand() % 6 + 1;
    if(b > a) win++;
    tot++;
  }

  cout << fixed << setprecision(9) << (double)win/tot << endl;
  return 0;
}