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

int main() {
    int a, b, c;
    cin >> a >> b >> c;
    int sides[3] = {a, b, c};
    sort(sides, sides + 3);
    if (sides[0] * sides[0] + sides[1] * sides[1] == sides[2] * sides[2]) {
        double area = 0.5 * sides[0] * sides[1];
        cout << fixed << setprecision(1) << area << endl;
    } else {
        cout << "No" << endl;
    }
    return 0;
}    
/**************************************************************
	Problem: 1047
	User: fandaohan
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2076 kb
****************************************************************/