#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep3(i, l, n) for (int i = l; i < n; ++i)
#define chmax(a, b) a = (a >= b ? a : b)
#define chmin(a, b) a = (a <= b ? a : b)
#define out(a) cout << a << endl
#define outa(a, n) rep(_, n) cout << a[_] << " "; cout << endl
#define SZ(v) (int)v.size()
#define inf (int)(1e9+7)
#define abs(x) (x >= 0 ? x : -(x))

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int b1, b2, b3;
    cin >> b1 >> b2 >> b3;
    if (b2 == b1) {
        out(b1);
        return 0;
    }
    double r = (double)(b3 - b2) / (b2 - b1);
    double d = b3 - r * b2;
    double tmp = r * b3 + d;
    if (tmp > 0) tmp += 0.5;
    else tmp -= 0.5;
    out((ll)tmp);
    // 11.5 -> 12
    // 11.4 -> 11
    // -11.4 -> -11
    // -11.5 -> -12
    
}