#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef int _loop_int;
#define REP(i,n) for(_loop_int i=0;i<(_loop_int)(n);++i)
#define FOR(i,a,b) for(_loop_int i=(_loop_int)(a);i<(_loop_int)(b);++i)
#define FORR(i,a,b) for(_loop_int i=(_loop_int)(b)-1;i>=(_loop_int)(a);--i)

#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define DEBUG_VEC(v) cout<<#v<<":";REP(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

#define CHMIN(a,b) a=min((a),(b))
#define CHMAX(a,b) a=max((a),(b))

// mod
const ll MOD = 1000000007ll;
#define FIX(a) ((a)%MOD+MOD)%MOD

// floating
typedef double Real;
const Real EPS = 1e-11;
#define EQ0(x) (abs(x)<EPS)
#define EQ(a,b) (abs(a-b)<EPS)
typedef complex<Real> P;

int main(){
  ll a,b,c;
  cin>>a>>b>>c;
  // c = rb+d
  // b = ra+d
  // c-b = r(b-a)
  // r = (c-b) / (b-a)
  // d = b - ra
  if(c-b == b-a){
    // r = 1
    ll d = b - a;
    ll nxt = c + d;
    cout << nxt << endl;
  }else{
    ll d_ba = b * (b-a) - a * (c-b);
    ll nxt_ba = c * (c-b) + d_ba;
    ll nxt = nxt_ba / (b-a);
    cout << nxt << endl;
  }
  return 0;
}