#include<stdio.h>

void cpy(unsigned long long int f[],unsigned long long int t[]){
	int i;
	for(i=0;i<=63;i++){t[i] = f[i];}
}

void res(unsigned long long int d[]){
	int i;
	for(i=0;i<=63;i++){d[i]=0;}
}

unsigned long long int sixpow(int t){
	int i;
	unsigned long long int m=1;
	for(i = 1;i <= t;i++){m*=6;}
	return m;
}

int main(void){
	unsigned long long int x[64]={0},y[64]={0},mx[64]={0},my[64]={0};
	int n,k,i,j,a;
	unsigned long long int t,wt;
	double ans;
	scanf("%d%d",&n,&k);
	x[0]=1;
	mx[0]=1;
	for(i = 1;i <= k;i++){
		res(y);
		res(my);
		for(j = 0;j <= 57;j++){
			for(a = 4;a <= 6;a++){my[j+a]+=(mx[j] * 2);}
			for(a = 1;a <= 6;a++){y[j+a]+=(x[j]);}
		}
		cpy(y,x);
		cpy(my,mx);
	}
	for(i = k+1;i <= n;i++){
		res(y);
		res(my);
		for(j = 0;j <= 57;j++){
			for(a = 1;a <= 6;a++){my[j+a]+=(mx[j]);}
			for(a = 1;a <= 6;a++){y[j+a]+=(x[j]);}
		}
		cpy(y,x);
		cpy(my,mx);
	}
	t = sixpow(n);
	t = t * t;
	for(i=1;i<=62;i++){
		for(j = i+1;j <= 63;j++){
			wt+=(x[i]*mx[j]);
		}
	}
	ans = wt;
	ans/=t;
	printf("%lf\n",ans);
	return 0;
}