#include<bits/stdc++.h>
using namespace std;
int main()
{
	int a,b,c;
	cin>>a>>b>>c;
	if(a>b)
	{
		int temp=a;
		a=b;
		b=temp;
	}
	if(b>c)
	{
		int temp=b;
		b=c;
		c=temp;
	}
	if(a>b)
	{
		int temp=a;
		a=b;
		b=temp;
	}
	if(b-a==c-b) cout<<"Yes";
	else cout<<"No";
	return 0;
}