#include <bits/stdc++.h>
#define FOR(i,bg,ed) for(ll i=(bg);i<(ed);i++)
#define REP(i,n) FOR(i,0,n)
#define MOD 1000000007
#define int long long
using namespace std;
typedef long long ll;
const int INF = 1e9;



signed main()
{
    int b1, b2, b3;
    cin >> b1 >> b2 >> b3;

    cout << (b3 - b2) * (b3 - b2) / (b2 - b1) + b3 << endl;
}