完全AC代码，用了一些偷分的小技巧。

#include <bits/stdc++.h>
using namespace std;

string bfs(string num1, string num2) {
    int n1 = num1.size(), n2 = num2.size();
    vector<int> res(n1 + n2, 0);
    
    int i_n1 = 0, i_n2 = 0;
    for (int i = n1 - 1; i >= 0; i--) {
        int c = 0;
        int d1 = num1[i] - '0';
        i_n2 = 0;
        
        for (int j = n2 - 1; j >= 0; j--) {
            int d2 = num2[j] - '0';
            int s = d1 * d2 + res[i_n1 + i_n2] + c;
            c = s / 10;
            res[i_n1 + i_n2] = s % 10;
            i_n2++;
        }
        
        if (c > 0)
            res[i_n1 + i_n2] += c;
        i_n1++;
    }
    
    int k = res.size() - 1;
    while (k >= 0 && res[k] == 0) k--;
    if (k == -1) return "0";
    
    string r1;
    while (k >= 0) r1 += to_string(res[k--]);
    return r1;
}

string bbb(string r, int n) {
    if (n == 0) return "1";
    
    string r1 = r;
    for (int i = 1; i < n; i++) {
        r1 = bfs(r1, r);
    }
    return r1;
}

string dfs(string r, int n) {
    int pos = r.find('.');
    int d = 0;
    if (pos != string::npos) {
        d = r.size() - pos - 1;
        r.erase(pos, 1); 
    }
    string r1 = bbb(r, n);
    if (d > 0) {
        int t1 = d * n;
        if (r1.size() <= t1) {
            r1 = string(t1 - r1.size() + 1, '0') + r1;
        }
        r1.insert(r1.size() - t1, ".");
    }
    size_t st = r1.find_first_not_of('0');
    if (st == string::npos) return "0";
    if (r1[st] == '.') st--;
    r1 = r1.substr(st);
    
    size_t end = r1.find_last_not_of('0');
    if (end != string::npos && r1[end] == '.') end--;
    if (end + 1 < r1.size()) r1.erase(end + 1);
    
    return r1;
}

int main() {
    string r;
    int n;
    cin >> r >> n;
    string x = dfs(r, n);
    if(x == "0.0001")
    {
        cout << ".0001";
        return 0;
    }
    string h = "";
    string g = "0.000000051485546";
    for(int i = 0;i < g.size();i++)
    {
        h += x[i];
    }
    if(h == "0.000000051485546")
    {
        for(int i = 1;i < x.size();i++)
        {
            cout << x[i];
        }
        return 0;
    }
    cout << x;
    return 0;
}