#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <array>
#include <map>
#include <stack>
#include <queue>
#include <set>
#include <cmath>
#include <numeric>

using namespace std;


int main() {

    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

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

    double r = (b3 - b2) / (b2 - b1);

    long result = static_cast<long>(b3 + (b3 - b2) * r);

    cout << result << "\n";

}