简单

#include <iostream>
#include <vector>
#include <cmath>
#include <iomanip>

using namespace std;

int main() {
int n, m;
cin >> n >> m;

// 边界情况：只有1人时必赢
if (n == 1) {
    cout << fixed << setprecision(9) << 1.0 << endl;
    return 0;
}

// 初始化k=1的情况：prev_dp[0]对应dp[1][1]
vector<double> prev_dp(1, 1.0);

// 从k=2开始递推到k=n
for (int k = 2; k <= n; ++k) {
    // 计算sum_val = sum_{i=1 to k-1} (0.5)^((k-1)-i) * dp[k-1][i]
    double sum_val = 0.0;
    for (int i = 1; i < k; ++i) {  // i是1-based位置
        int t = (k - 1) - i;       // 指数
        sum_val += pow(0.5, t) * prev_dp[i - 1];
    }
    
    // 计算dp[k][1]（对应curr_dp[0]）
    double denominator = 6 * (1 - 1 / pow(2, k));
    double curr_dp0 = (1 + sum_val) / denominator;
    vector<double> curr_dp;
    curr_dp.push_back(curr_dp0);
    
    // 计算dp[k][2]到dp[k][k]
    for (int p = 2; p <= k; ++p) {
        double term1 = 0.5 * curr_dp[p - 2];  // dp[k][p-1]
        double term2 = (1.0 / 3) * prev_dp[p - 2];  // dp[k-1][p-1]
        curr_dp.push_back(term1 + term2);
    }
    
    // 更新prev_dp为当前k的结果
    prev_dp = move(curr_dp);
}

// 输出结果，精确到小数点后9位
cout << fixed << setprecision(9) << prev_dp[m - 1] << endl;

return 0;

}