diff --git a/atcoder/abc144/A/main.cpp b/atcoder/abc144/A/main.cpp
new file mode 100644
index 00000000..dbf2f9e7
--- /dev/null
+++ b/atcoder/abc144/A/main.cpp
@@ -0,0 +1,21 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+using ll = int64_t;
+using ff = long double;
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0); cout.tie(0);
+
+    int A, B;
+    cin >> A >> B;
+
+    if (A >= 10 || B >= 10) {
+        cout << -1 << endl;
+    } else {
+        cout << (A * B) << endl;
+    }
+
+    return 0;
+}
\ No newline at end of file
diff --git a/atcoder/abc144/B/main.cpp b/atcoder/abc144/B/main.cpp
new file mode 100644
index 00000000..77f666e1
--- /dev/null
+++ b/atcoder/abc144/B/main.cpp
@@ -0,0 +1,25 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+using ll = int64_t;
+using ff = long double;
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0); cout.tie(0);
+
+    int N;
+    cin >> N;
+    bool found = false;
+    for (int x = 1; x <= 9; ++x) {
+        for (int y = 1; y <= 9; ++y) {
+            if (x * y == N) {
+                found = true;
+                break;
+            }
+        }
+    }
+    cout << (found ? "Yes" : "No") << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/atcoder/abc144/C/main.cpp b/atcoder/abc144/C/main.cpp
new file mode 100644
index 00000000..1eb85533
--- /dev/null
+++ b/atcoder/abc144/C/main.cpp
@@ -0,0 +1,27 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+using ll = int64_t;
+using ff = long double;
+
+ll solve(ll N) {
+    ll ans = N;
+    for (ll x = 1; x * x <= N; ++x) {
+        if (N % x == 0) {
+            ll y = N / x;
+            ans = min(ans, (x-1)+(y-1));
+        }
+    }
+    return ans;
+}
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0); cout.tie(0);
+
+    ll N;
+    cin >> N;
+    cout << solve(N) << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/atcoder/abc144/D/main.cpp b/atcoder/abc144/D/main.cpp
new file mode 100644
index 00000000..14829981
--- /dev/null
+++ b/atcoder/abc144/D/main.cpp
@@ -0,0 +1,23 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+using ll = int64_t;
+using ff = long double;
+
+int main() {
+    ios_base::sync_with_stdio(false);
+    cin.tie(0); cout.tie(0);
+
+    int a, b, x;
+    cin >> a >> b >> x;
+    ff theta;
+    if (2 * x >= a * a * b) {
+        theta = atan2(2 * a * a * b - 2 * x, a * a * a);
+    } else {
+        theta = M_PI / ff(2.0) - atan2(2 * x, a * b * b);
+    }
+    theta = theta * ff(180) / M_PI;
+    cout << fixed << setprecision(7) << theta << endl;
+
+    return 0;
+}
\ No newline at end of file