#include <iostream>
#include <stdio.h>
#include <string.h>
#include <queue>
#include <math.h>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <stack>

using namespace std;

#define LL long long
const int N =1e5+10;
const int INF =0x3f3f3f3f;

int main(){
    double a,b,c,p;
    cin>>a>>b>>c;
    p=(a+b+c)/2;
    cout<<fixed<<setprecision(2)<<sqrt(p*(p-a)*(p-b)*(p-c))<<endl;
    return 0;
}