#include <algorithm>
#include <iostream>
using namespace std;

bool ans;
int A[5];

int main(){
	cin >> A[1] >> A[2] >> A[3];
	sort(A + 1,A + 1 + 3);
	if (A[3] - A[2] == A[2] - A[1]) cout << "Yes\n";
	else cout << "No\n";
	return 0;
}
#include<bits/stdc++.h>
using namespace std;
 #define mod 1000000007
 #define ll long long int
 #define pb push_back
  int main()
 {    ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    ll t=1;
 //  cin>>t;
         while(t--){
    ll i;
    ll a,b,c,d;
     cin>>a>>b>>c>>d;

       cout<<b-c;
         }
 }
