#include <bits/stdc++.h> #define REP(i,n,N) for(int i=(n);i<(int) N;i++) #define p(s) cout<<(s)<<endl using namespace std; double dp1[15][100]; double dp2[15][100]; int main(void){ int N,K; cin>>N>>K; dp1[0][0]=dp2[0][0]=1; REP(i,0,N) REP(j,0,i*6+1) REP(k,1,7) dp1[i+1][j+k]+=dp1[i][j]/6.0; REP(i,0,N) REP(j,0,i*6+1) { if(i<K) REP(k,4,7) dp2[i+1][j+k]+=dp2[i][j]/3.0; else REP(k,1,7) dp2[i+1][j+k]+=dp2[i][j]/6.0; } double ans=0; REP(i,0,N*6+1) REP(j,i+1,N*6+1) ans+=dp1[N][i]*dp2[N][j]; printf("%.5lf",ans); return 0; }