#include using namespace std; const int MAX_N = 20; double taro[MAX_N][MAX_N * 6], jiro[MAX_N][MAX_N * 6]; int main() { int n, k; cin >> n >> k; taro[0][0] = 1; jiro[0][0] = 1; for (auto i = 1; i <= n; i++) { for (auto sum = 1; sum <= n * 6; sum++) { for (auto d = 1; d <= 6; d++) { auto dice = (i <= k && d <= 3) ? d + 3 : d; if (sum - dice >= 0) { taro[i][sum] += taro[i - 1][sum - dice] / 6.0; } if (sum - d >= 0) { jiro[i][sum] += jiro[i - 1][sum - d] / 6.0; } } } } // 計算を軽くするため二郎君の分をsum以下の目の出し方とする for (auto sum = 1; sum <= n * 6; sum++) { jiro[n][sum] += jiro[n][sum - 1]; } auto ans = 0.0; for (auto sum = 1; sum <= n * 6; sum++) { ans += taro[n][sum] * jiro[n][sum - 1]; } cout << ans << endl; return 0; }