#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define endl "\n"
#define all(v) begin(v),end(v)
#define pb push_back
#define fr first
#define sc second
#define si(s) (int)s.size()
#define rep(i,a,b) for(int i=a;i<b;i++)
#define dig(a) fixed<<setprecision(a)
#define fast ios_base::sync_with_stdio(false); cin.tie(NULL)
const int M = 1e9+7;
ll power(ll a, ll n) { 
ll res = 1; 
while (n) { 
if (n % 2) {res = (res * a) % M;} 
n >>= 1; a = (a * a) % M;} 
return res;
}

const int N  = 1e5+5;

void solve(){

	int a,b,c,d;
	cin>>a>>b>>c>>d;
	cout<<b-c;
}
int main(){
	fast;

	// #ifndef ONLINE_JUDGE
	// 	freopen("input.txt","r",stdin);
	// 	freopen("output.txt","w",stdout);
	// #endif
 	
 	int tt=1; //cin>>tt;
 	while(tt--){
 		solve();
 	}
	return 0;
 	
}


#include<bits/stdc++.h>
#define all(x) (x).begin(),(x).end()

using ll = long long;
using ld = long double;
using namespace std;

const ll inf = 2e18;
const ll mod = 1e9 + 7;
const ll N = 2e5 + 5;

int a, b, c;

void code() {
    cin >> a >> b >> c;

    vector<int> v{a, b, c};
    sort(all(v));
    if (v[2] - v[1] == v[1] - v[0]) {
        cout << "Yes\n";
        return;
    }

    cout << "No\n";
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int t = 1;
    // cin>>t;

    while (t-- > 0) {
        code();
    }
}