#include<bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
  double b1,b2,b3;
  cin>>b1>>b2>>b3;
  double r=(b3-b2)/(b2-b1);
  double d=b3-r*b2;
  cout<<(int)round(r*b3+d)<<endl;
  return 0;
}