#include<iostream>
#include<string>
#include<algorithm>

using namespace std;

long arr[30], A , i, C;

int main()
{
while (cin >> arr[i])
{
i++;
}
sort (arr , arr + i);
A = arr[1] - arr[0];
for (int b = 1 ; b < i ; b++)
{
  if (arr[b] - arr[b-1] != A)
  {
  cout << "No";
  return 0 ;
  }
}
cout << "Yes";

  return 0;
}