#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <algorithm>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>

using namespace std;


int main()
{
    int a,b,c;
    cin >> a >> b >> c;
    if(a + c == b * 2)
        cout << "Yes";
    else
        cout << "No"
    return 0;
}
