/* -*- coding: utf-8 -*-
 *
 * 538.cc: No.538 N.G.S. - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

typedef long long ll;

struct Frac {
  ll n, d;
  Frac(): n(0), d(1) {}
  Frac(ll _n): n(_n), d(1) {}
  Frac(ll _n, ll _d): n(_n), d(_d) {}

  Frac normalize() {
    ll g = __gcd(abs(n), abs(d));
    n /= g, d /= g;
    if (d < 0) n = -n, d = -d;
    return *this;
  }

  Frac operator+(const Frac f) {
    return Frac(n * f.d + f.n * d, d * f.d).normalize();
  }
  Frac operator-(const Frac f) {
    return Frac(n * f.d - f.n * d, d * f.d).normalize();
  }
  Frac operator*(ll k) {
    return Frac(n * k, d).normalize();
  }

  void print() { printf("%lld/%lld", n, d); }
};

/* global variables */

/* subroutines */

/* main */

// b1=r*b0+d..(1), b2=r*b1+d..(2)
// (2)-(1).. b2-b1=r*(b1-b0) -> r=(b2-b1)/(b1-b0)

int main() {
  ll b0, b1, b2;
  cin >> b0 >> b1 >> b2;

  Frac r(b2 - b1, b1 - b0);
  r.normalize();

  Frac d = Frac(b2) - r * b1;
  //printf("r=%lld/%lld,d=%lld/%lld\n", r.n, r.d, d.n, d.d);

  Frac b3 = r * b2 + d;
  printf("%lld\n", b3.n);
  return 0;
}