#include <iostream>
#include <math.h>
using namespace std;
int main(){
	double a,b,c;
	cin>>a>>b>>c;
	double p=(a+b+c)/2;
	double S=sqrt(p*(p-a)*(p-b)*(p-c));
	printf("%.2f",S);
	return 0; 
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    double a,b,c;
    cin >> a >> b >> c;
    double p = (a + b + c)/2;
    double sum = p * (p-a)*(p-b)*(p-c);
    sum = sqrt(sum);
    printf("%.2lf\n",sum);
}

#include <bits/stdc++.h>

using namespace std;

int main()
{
	double a, b, c, p, m;

	cin >> a >> b >> c;

	p = (a + b + c) / 2;

	m = p * (p - a) * (p - b) * (p - c);

	cout << fixed << setprecision(2) << sqrt(m);

	return 0;
}

#include<iostream>

#include<cmath>

#include<iomanip>

using namespace std;

int main()

{

double a,b,c,d,p;

cin>>a>>b>>c;

p=(a+b+c)/2;

d=p*(p-a)(p-b)(p-c);

cout << setiosflags (ios::fixed<<setprecision(2);

cout <<sqrt(d);

return 0;

}

#include<iostream>
#include<cstdio>
#include<string>
#include<bits/stdc++.h>
#define LL long long
using namespace std;
const int INF=0x3f3f3f3f;
const int N=2e5+10;
double a,b,c;
int main(){
	cin>>a>>b>>c;
	double p=(a+b+c)/2;
	printf("%.2f",sqrt(p*(p-a)*(p-b)*(p-c)));
}

#include <iostream> #include <stdio.h> #include <string.h> #include <queue> #include <math.h> #include <vector> #include <algorithm> #include <iomanip> #include <stack> #include <bits/stdc++.h> using namespace std; int main(){ double a,b,c,p,m; cin>>a>>b>>c; p=(a+b+c)/2; double sum; m= p * (p - a) * (p - b) * (p - c); cout << fixed << setprecision(2) << sqrt(m);

return 0;

}

#include <stdio.h> #include <iostream> #include <math.h> using namespace std; int main() { double a , b , c , p; cin >> a >> b >> c; p = (a + b + c)/2; double num = p*(p - a)(p - b)(p - c); double s = sqrt ( num ); printf("%.2lf",s);

}

#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;
}