#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
using namespace std;
using ll = long long;
using P = pair<int, int>;

int main() {   
    double sx, sy, gx, gy;
    cin >> sx >> sy >> gx >> gy;
    double ty = sy + gy;
    double tx;
    if(sx >=0 && gx >= 0){
      if(sx > gx){
        tx = sx - gx;
      }
      else{
        tx = gx - sx;          
      }
    }
    else if(sx < 0 && gx >=0){
        tx = -sx + gx;
    }
    else if(sx >=0 && gx < 0){
        tx = sx - gx;
    }
    else{
      if(sx > gx){
        tx = sx - gx;
      }
      else{
        tx = gx - sx;          
      }
    }
    double ans;
    if(sx < gx){
        ans = sx + tx*(sy / ty);
    }
    else{
        ans = sx - tx*(sy / ty);
    }
  printf("%.10f\n", ans);
}
/*     Har Har Mahadev    */
//cout<<fixed<<setprecision(11)<<ans<<"\n";
//cin.ignore();getline(cin,s,'\n');
#include <bits/stdc++.h>
using namespace std; 
typedef long long ll;
typedef long double ld;
typedef vector<ll> vll;
typedef pair<ll,ll> pll;
#define lab(i,a,b) for(i=a;i<=b;i++)
#define bal(i,a,b) for(i=b;i>=a;i--)
#define ff first 
#define ss second 
#define pb push_back
#define se(v) v.begin(), v.end()
#define fst ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
#define tc ll t;cin>>t;while(t--) 
#define fceil(a,b) ceil((ld)a/(ld)b)
#define dis(v) for(auto it:v)cout<<it<<" "
#define yep cout<<"Yes\n"
#define nope cout<<"No\n"
bool isPrime(ll n){if(n <= 1)return false;if(n <= 3)return true;if(n%2==0||n%3==0)return false;for(ll i=5;i*i<= n;i=i+6)if(n%i==0||n%(i+2)==0)return false;return true;}
bool cmp(pll &a, pll &b){ if(a.ss == b.ss)return a.ff < b.ff;return a.ss < b.ss;}
const ll MOD = 1e9 + 7;
ll powerLL(ll x, ll n){ll result = 1;while (n){if (n & 1)result = result * x % MOD;n = n / 2;x = x * x % MOD;}return result;}
int main() 
{ 
    fst
    ll n,m,i,j,k,f,sum,ans,x,y,z;
    //tc
    {
      m=0,i=0,j=0,f=0,sum=0,x=0,y=0,z=0,ans=0;
      ll a[3];
      cin>>a[0]>>a[1]>>a[2];
      sort(a,a+3);
      if(2*a[1]==a[0]+a[2])yep;
      else nope;
    }
    return 0; 
} 