#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(ri,n) for(int ri = (int)(n-1); ri >= 0; ri--)
#define rep2(i,x,n) for(int i = (int)(x); i < (int)(n); i++)
#define rrep2(ri,x,n) for(int ri = (int)(n-1); ri >= (int)(x); ri--)
#define repit(itr,x) for(auto itr = x.begin(); itr != x.end(); itr++)
#define rrepit(ritr,x) for(auto ritr = x.rbegin(); ritr != x.rend(); ritr++)
#define ALL(x) x.begin(), x.end()
using ll = long long;
using namespace std;

int main() {
  int a, b, c;
  cin >> a >> b >> c;
  double a2 = a/2.0, b2 = b/2.0, c2 = c/2.0;
  double s = (a2+b2+c2)/2.0;
  double ans = sqrt(s*(s-a2)*(s-b2)*(s-c2));
  cout << fixed << setprecision(10) << ans << endl;
  return 0;
}