include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;

int main()
{
    double a,b,c;
    cin >> a >> b >> c;
    double p = (a + b + c) / 2;
    double s = p * (p - a)*(p - b)*(p - c);
    s = sqrt(s) + 0.05;//该目的为四舍五入
    cout << fixed << setprecision(1) << s << endl;

    
    return 0;
}