#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

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

  ll p = b3-b2;
  ll q = b2-b1;
  ll t = q*b2 - p*b1;
  ll s = q;

  cout << (s*b3*p + t*q)/(q*s) << endl;
  
  return 0;
}