#include <bits/stdc++.h>
using namespace std;
//#include <atcoder/all>
//using namespace atcoder;
using ll=long long;
using Graph=vector<vector<int>>;
#define MAX 100001
#define INF 1000000000000000000
#define MOD 1000000007

int main(){
  vector<int> A(3);
  for(int i=0;i<3;i++){
    cin>>A[i];
  }
  sort(A.begin(),A.end());
  if(A[2]-A[1]==A[1]-A[0]){
    cout<<"Yes"<<endl;
  }else{
    cout<<"No"<<endl;
  }
}

/*
	JAI JAGANNATH!
*/
//@Author : zanj0

#include<bits/stdc++.h>
using namespace std;

#define int 			long long int

#define ff              first
#define ss              second
#define pb              push_back
#define MOD             1000000007
#define inf             1e18
#define ps(x,y)         fixed<<setprecision(y)<<x
#define w(x)            int x; cin>>x; while(x--)
#define endl       		"\n"
#define timetaken cerr<<"Time : "<<1000*(long double)clock()/(long double)CLOCKS_PER_SEC<<"ms\n"

void zanj0()
{
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#ifdef LOCAL
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
}
void solve() {
	vector <int> v(3);
	for (int i = 0, x; i < 3; i++) {
		cin >> v[i];
	}
	sort(v.begin(), v.end());
	if (v[0] == v[1]) {
		cout << v.back() << endl;
	} else if (v[1] == v.back()) {
		cout << v[0] << endl;
	} else {
		cout << 0 << endl;
	}

}
int32_t main()
{
	zanj0();
	solve();
	timetaken;
	return 0;
}