#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vd = vector<double>;
using vvd = vector<vd>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vs = vector<string>;

const int INF = (1 << 30) - 1;
const ll INF64 = ((ll)1 << 62) - 1;
const double PI = 3.1415926535897932384626433832795;

const int dx[] = { -1, 0, 1, 0 };
const int dy[] = { 0, 1, 0, -1 };

int gcd(int x, int y) { return y ? gcd(y, x % y) : x; }
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
int lcm(int x, int y) { return x / gcd(x, y) * y; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

int main() {
	//ios::sync_with_stdio(false);
	//cin.tie(0);

	long double b1, b2, b3;
	cin >> b1 >> b2 >> b3;

	/*printf("%ld\n", (b3 * b3 + b2 * b2 - b2 * b3 - b1 * b3) / (b2 - b1));*/
	cout << (b3 * b3 + b2 * b2 - b2 * b3 - b1 * b3) / (b2 - b1) << endl;
	return 0;
}