#include<bits/stdc++.h>
using namespace std;
int main()
{
  long long a,b,c;
  cin>>a>>b>>c;
  vector<long long>vec;
  vec.push_back(a);vec.push_back(c);vec.push_back(b);
  sort(vec.begin(),vec.end());
  if(vec[1]-vec[0]==vec[2]-vec[1])
     {
       cout<<"Yes"<<endl;
     }
     else 
     {
       cout<<"No"<<endl;
     }
}
#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[8]={-1,0,1,0,1,1,-1,-1};
const ll dx[8]={0,-1,0,1,1,-1,1,-1};
template <typename T> inline bool chmax(T &a, T b) {
  return ((a < b) ? (a = b, true) : (false));
}
template <typename T> inline bool chmin(T &a, T b) {
  return ((a > b) ? (a = b, true) : (false));
}
int main(){
  vl v(3);rep(i,3)cin >> v[i];
  sort(all(v));
  if(v[2]-v[1]==v[1]-v[0])cout << "Yes" <<endl;
  else cout << "No" <<endl;
}   