#include <stdio.h>
#include <stdlib.h>
#include <time.h>

const int M = 1e7L;

// eval"p (1..1e6).count{(1..%d).map{|i|rand(6)-rand(i>%d?6:3..5)}.sum<0}/1e6"%[*$<]
int main(void)
{
  int N, K;
  scanf("%d\n", &N);
  scanf("%d\n", &K);
  srand(time(NULL));

  int count = 0;
  for (int i = 0; i < M; ++i) {
    int taro = 0, jiro = 0;
    for (int j = 0; j < N; ++j) {
      if (j < K)
        taro += 4 + rand()%3;
      else
        taro += 1 + rand()%6;
      jiro += 1 + rand()%6;
    }
    if (taro > jiro)
      ++count;
  }
  printf("%f\n", ((double)count) / M);
}