//Radhe Radhe
#include<bits/stdc++.h>
#define FASTIO_  ios_base:: sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define ll long long

#define mod 1000000007
#define ld long double
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define itr(i,n)    for(ll i=0; i<n; i++)
#define itr_ab(i,a,b)    for(ll i=a; i<=b; i++)
#define itrV(i,n)    for(ll i=0; i<v.size(); i++)
#define fixed cout.setf(ios::fixed);
#define precise cout.precision(15);
#define yes cout<<"Yes"<<'\n'
#define no cout<<"No"<<'\n'
#define en '\n'
#define Dont_Quit int main(void)
#define Avada_Kedavra return 0;
using namespace std;


Dont_Quit
{
    FASTIO_
    ll  tc,n,m,x,i,j,d;
    string s;
    tc=1;
    while(tc--)
    {
        ll a[3];
        cin>>a[0]>>a[1]>>a[2];
        sort(a,a+3);
        if(a[2]-a[1]==a[1]-a[0])
            yes;
        else no;
    }

    Avada_Kedavra
}




#include<bits/stdc++.h>
using namespace std;
int main(){
    int a,b,c;
    cin>>a>>b>>c;
    int arr[]={a,b,c};
    int count=0;
    sort(arr,arr+3);
        if(arr[1]-arr[0]==arr[2]-arr[1])count++;
    if(count==1)cout<<"Yes"<<endl;
    else cout<<"No"<<endl;
   return 0; 
}