#include<iostream>
#include<math.h>
#include<vector>
#include <array>
#include <algorithm>
#include <queue>
#include <numeric>
#include <map>

using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) printf(__VA_ARGS__)

typedef pair<int, int> pos;
int pos::*x = &pos::first;
int pos::*y = &pos::second;

int dxy[] = {0, 1, 0, -1, 0};

/*================================*/

signed main()
{
    int N, K;
    cin >> N >> K;
    rand();
    int win = 0;
    int trynum = 10000000;
    REP(i,trynum) {
        int taro = 0;
        REP(i,N-K) {
            taro += 1 + rand() % 6;
        }
        REP(i,K) {
            taro += 4 + rand() % 3;
        }
        int jiro = 0;
        REP(i,N) {
            jiro += 1 + rand() % 6;
        }
        win += (taro > jiro);
    }
    out("%.10f\n", 1.0 * win / trynum);

    return 0;
}