#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#include <list>
#include <atcoder/all>
#define popcount __builtin_popcount
using namespace std;
using namespace atcoder;
typedef long long ll;
typedef pair<int, int> P;

int main()
{
    double a, b, c;
    double a0=2, b0=4, c0=5, s0=0.9499177596;
    cin>>a>>b>>c;
    auto calc=[&](double x, double y, double z){
        double s=(x+y+z)/2;
        return sqrt(s*(s-x)*(s-y)*(s-z));
    };
    printf("%.8lf\n", s0/calc(a0, b0, c0)*calc(a, b, c));
    return 0;
}