D - 2-variable Function

https://atcoder.jp/contests/abc246/submissions/30655016

AtCoder/ABC246/D/D.cpp

@@ -0,0 +1,31 @@
+#include <cmath>
+#include <iostream>
+#include <limits>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+long long n, a, b, ans = std::numeric_limits<long long>::max();
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> n;
+
+    if (!n) {
+        cout << 0 << endl;
+        exit(0);
+    }
+
+    while (std::pow(a, 3) * 4 < n) b = ++a;
+    while (b) {
+        while (b && (a + b - 1) * (a * a + (b - 1) * (b - 1)) >= n) b--;
+        ans = std::min(ans, (a + b) * (a * a + b * b));
+        a++;
+    }
+
+    cout << ans << endl;
+
+    return 0;
+}