#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>
#include <random>

#define REP(i,n) for(int (i)=0;(i)<(n);(i)++)
#define FOR(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
#define RREP(i,a) for(int (i)=(a)-1;(i)>=0;(i)--)
#define FORR(i,a,b) for(int (i)=(a)-1;(i)>=(b);(i)--)
#define PI acos(-1.0)
#define DEBUG(C) cout<<C<<endl;
#define VI vector<int>
#define VII vector<VI>
#define VL vector<LL>
#define VLL vector<VL>
#define VD vector<double>
#define VDD vector<VD>
#define PII pair<int,int>
#define PDD pair<double,double>
#define PLL pair<LL,LL>
#define VPII vector<PII>
#define ALL(a) (a).begin(),(a).end()
#define SORT(a) sort(ALL(a))
#define REVERSE(a) reverse(ALL(a))
#define MP make_pair
#define FORE(a,b) for(auto &&a:b)
#define FIND(s,n) s.find(n)!=s.end()

using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
const int INF=1e9;
const int MOD=INF+7;

int N, K;
random_device rnd;

int t(void) {
    int res =0;
    REP (i, N) {
        res += (rnd()%6)+1;
    }
    return res;
}
int j(void) {
    int res = 0;
    REP(i, N) {
        if(i<K) res += (rnd()%3)+4;
        else res += (rnd()%6)+1;
    }
    return res;
}

int main (void) {
    cin >> N >> K;
    int tcnt = 0, jcnt = 0;
    REP(i,1e5){
        int tt = t();
        int jj = j();
        if(tt>jj) tcnt ++;
        if(jj>tt) jcnt ++;
    }
    double ans = (double)((double)jcnt/(double)1e5);
    cout << fixed << setprecision(5) << ans << endl;
}