#include <vector>
#include <random>
#include <cstdio>
using namespace std;
int main(){
    int N,K,T=999999,S=0,I=0;
    scanf("%d%d",&N,&K);
    uniform_int_distribution<int>g(1,6),h(4,6);
    mt19937_64 e(0);
    for(;I<T;I++){
        int a=0,b=0,i=0;
        for(;i<N;i++)a+=g(e),b+=i<K?h(e):g(e);
        if(a<b)S++;
    }
    printf("%f\n",S*1.0/T);
}