diff --git a/LibreOJ/6/6.cpp b/LibreOJ/6/6.cpp
new file mode 100644
index 00000000..2d3b70c1
--- /dev/null
+++ b/LibreOJ/6/6.cpp
@@ -0,0 +1,31 @@
+#include "interaction.h"
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n;
+vector<int> ans;
+
+int main() {
+    n = get_num();
+    for (int i = 0; i < n; i++) {
+        int l = 0, r = 1000000;
+
+        while (l <= r) {
+            int mid = (l + r) >> 1, feedback = guess(i, mid);
+
+            if (!feedback) {
+                ans.emplace_back(mid);
+                break;
+            } else {
+                if (feedback > 0) {
+                    r = mid - 1;
+                } else {
+                    l = mid + 1;
+                }
+            }
+        }
+    }
+    submit(ans);
+    return 0;
+}
\ No newline at end of file
diff --git a/LibreOJ/6/interaction.h b/LibreOJ/6/interaction.h
new file mode 100644
index 00000000..25dce1f3
--- /dev/null
+++ b/LibreOJ/6/interaction.h
@@ -0,0 +1,27 @@
+#include <iostream>
+#include <vector>
+
+int get_num() {
+    std::cout << "get_num" << std::endl
+              << std::flush;
+    int ret;
+    std::cin >> ret;
+    return ret;
+}
+
+int guess(int index, int x) {
+    std::cout << "guess " << index << " " << x << std::endl
+              << std::flush;
+    int ret;
+    std::cin >> ret;
+    return ret;
+}
+
+void submit(const std::vector<int>& result) {
+    std::cout << "submit ";
+    for (std::vector<int>::const_iterator iter = result.begin(); iter != result.end(); iter++) {
+        std::cout << *iter << " ";
+    }
+    std::cout << std::endl
+              << std::flush;
+}
diff --git a/LibreOJ/6/interactor.cpp b/LibreOJ/6/interactor.cpp
new file mode 100644
index 00000000..47233866
--- /dev/null
+++ b/LibreOJ/6/interactor.cpp
@@ -0,0 +1,71 @@
+#include <cstdlib>
+#include <fstream>
+#include <iostream>
+#include <vector>
+
+std::ofstream score("score.txt");
+
+template <typename T>
+inline void assert(const T& condition, const std::string& message) {
+    if (!condition) {
+        std::cerr << message << std::endl;
+        score << -1 << std::endl;
+        exit(0);
+    }
+}
+
+int main() {
+    std::ifstream datin("input");
+    int n, nguess = 0;
+    datin >> n;
+    std::vector<int> nums(n);
+    for (int i = 0; i < n; i++) {
+        datin >> nums[i];
+    }
+
+    while (true) {
+        std::string cmd;
+        std::cin >> cmd;
+        if (cmd == "get_num") {
+            std::cout << n << std::endl
+                      << std::flush;
+        } else if (cmd == "guess") {
+            nguess++;
+            int index, val;
+            assert(std::cin >> index >> val, "Invalid `index` or `val` in `guess` command!");
+            assert(0 <= index && index < n, "`index` must in [0, n)!");
+
+            if (val < nums[index]) {
+                std::cout << -1 << std::endl
+                          << std::flush;
+            } else if (val > nums[index]) {
+                std::cout << 1 << std::endl
+                          << std::flush;
+            } else {
+                std::cout << 0 << std::endl
+                          << std::flush;
+            }
+        } else if (cmd == "submit") {
+            bool wrongAnswer = false;
+            for (int i = 0; i < n; i++) {
+                int x;
+                assert(std::cin >> x, "Can't read the " + std::to_string(i) + "-th number!");
+
+                if (x != nums[i] && !wrongAnswer) {
+                    wrongAnswer = true;
+                    std::cerr << "First differ on the " + std::to_string(i) + "-th number!" << std::endl;
+                    score << 0 << std::endl;
+                }
+            }
+
+            if (!wrongAnswer) {
+                score << std::max(std::min(100.0, (950.0 - ((double)nguess / n - 100.0)) / 950.0 * 100.0), 0.0) << std::endl;
+                std::cerr << "nguess = " + std::to_string(nguess) << std::endl;
+            }
+
+            exit(0);
+        } else {
+            assert(false, "Invalid command `" + cmd + "`!");
+        }
+    }
+}