code:

#include<bits/stdc++.h>
using namespace std;
long double a,b,c;
long double ans;
int main(){
    cin>>a>>b>>c;
	if(a > b) swap(a, b);
	if(a > c) swap(a, c);
	if(b > c) swap(b, c);
    long double f1=max((long double)(0.00),c-b-a);
    long double f2=-c*c-b*b-a*a;
    printf("%0.1Lf",(f1*f1+f2)/2.000);
    return !true;
}