/**
   Bismillahir Rahmanir Raheem
   Author:Refatul Fahad
   Bangabandhu Sheikh Mujibur Rahman Science & Technology University, Gopalganj-8100.
**/

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

#define ll long long
#define ull unsigned long long
#define ff first
#define ss second
#define pb push_back
#define vi vector<int>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define grv(v) sort(v.begin(),v.end(),greater<int>())
#define sz(s)  (int)s.size()
#define all(s)  s.begin(),s.end()
#define fill(a,b) memset(a,b,sizeof(a))
#define mnv(v) *min_element(v.begin(),v.end())
#define mxv(v) *max_element(v.begin(),v.end())
#define countv(v,a) count(v.begin(),v.end(),a)
#define el "\n"
#define IOS  ios_base::sync_with_stdio(false),cin.tie(NULL)
#define pr(x) cerr << #x << " ** " << x << endl;

const int N = 1e5 + 5;
const ll M = (ll)1e9 + 7;
const ll inf=(ll)1e18;
const double pi=2*acos(0.0);
const double esp=1e-9;

int dx[]= {0,0,1,-1};
int dy[]= {1,-1,0,0};


int main() {

    //IOS;
    /// freopen("input.txt","r",stdin);
    /// freopen("output.txt","w",stdout);

    int test=1;
    //cin>>test;
    for(int cs=1; cs<=test; ++cs) {
        int a,b,c,d;
        cin>>a>>b>>c>>d;
        cout<<a*d-b*c<<el;
    }
    return 0;
}



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

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