#include <iostream>
#include <sstream>
#include <vector>
#include <algorithm>
#include <string>
#include <functional>
#include <numeric>
#include <ctype.h>
#include <cstdlib>
#include <string.h>
#include <cmath>
#include <cstdio>
#include <map>
#include <queue>
#include <utility>

using namespace std;

const int INF = 1000000007;
const double PI = acos(-1.0);
typedef long long ll;

int dp[300];

int main()
{
	ll b1, b2, b3;
	cin >> b1 >> b2 >> b3;
	
	cout << (b3 * (b3 - b2) + (b2 * b2 - b1 * b3)) / (b2 - b1) << endl;
}