feat(c): add hhcn

c/hhcn.c

@@ -0,0 +1,13 @@
+#include <stdio.h>
+#include <math.h>
+
+int main() {
+    long long a, b, c;
+    scanf("%lld %lld %lld", &a, &b, &c);
+
+    double numerator = 4.0 * (a * b + b * c + c * a);
+    double denominator = sqrt((double) (a * b * c));
+
+    printf("%.0f\n", numerator / denominator);
+    return 0;
+}