#include<iostream>

using namespace std;

int main(){
    int a,b,c;

    cin>>a>>b>>c;

    if(a>=1&&a<=100&&b>=1&&b<=100&&a>=1&&a<=100)
    if(b-a==c-b){
        cout<<"Yes"<<endl;
    }
    else{
        cout<<"No"<<endl;
    }
}
