#include <bits/stdc++.h>
using namespace std;
int main() {
  int a[1000], l[1000], x[1000], i = 0;
  double M[1000], m1, m2, c, d;
  while (scanf("%d%d%d", &a[i], &l[i], &x[i]) != EOF) {
    i++;
  }
  for (int j = 0; j < i; j++) {
    m1 = (double)(a[j] * l[j]) / 2;
    c = (double)((2 * x[j] * l[j]) + (x[j] * x[j])) / 4;
    d = sqrt(c);
    m2 = l[j] * d;
    M[j] = m1 + m2;
  }
  for (int j = 0; j < i; j++) {
    printf("%.10f\n", M[j]);
  }
  return 0;
}
