#include <bits/stdc++.h>
#define REP(i,n,N) for(int i=(n);i<(int) N;i++)
#define RREP(i,n,N) for(int i=N-1;i>=(int) n;i--)
#define p(s) cout<<(s)<<endl
#define DEBUG(x,y) cout<<#x<<": "<<x<<" , "<<#y<<": "<<y<<endl;
#define CK(n,a,b) ((a)<=(n)&&(n)<=(b))
#define F first
#define S second
typedef long long ll;
using namespace std;
const ll inf=1e5;

int b1,b2,b3;
int r;
bool flag;
int main(){
	cin>>b1>>b2>>b3;
	r=inf;
	REP(i,-1e5,1e5+1){
		if(i==0) continue;
		if(b3-b2 == i*(b2-b1)){
			r=i;
			flag=true;
			break;

		}
	}
	if(!flag){
		REP(i,-1e5,1e5+1){
			if(i==0) continue;
			if(i*(b3-b2) == (b2-b1)){
				r=i;
				break;
			}

		}
		p((b3-b1)/r+b2);
	}else{
		p(r*(b3-b1)+b2);
	}

	return 0;
}