#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using vb = vector<bool>;
using vi = vector<int>;
using vvi = vector<vector<int>>;
using vl = vector<long long>;
using vvl = vector<vector<long long>>;
using vc = vector<char>;
using vvc = vector<vector<char>>;
const long long MOD2 = 998244353LL;
const long long MOD = 1000000007LL;
const long long INF = 1LL<<60; 


int main(){
   double sx,sy,cx,cy;
   cin >> sx >> sy >> cx >> cy;
   cy *= -1;
   if(sx == cx)cout << sx << endl;
   else{
      double a = (cy-sy)/(cx - sx);
      double b = sy - a*sx;
      printf("%.15lf\n", -1.0*b/a);
   }
   return 0;
} 
#include<iostream>
using namespace std;
int main()
{
 int a,b,c;
  cin>>a>>b>>c;
  cout<<21-a-b-c<<endl;
  return 0;
}