#include <cassert>// c
#include <iostream>// io
#include <iomanip>
#include <fstream>
#include <sstream>
#include <vector>// container
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <algorithm>// other
#include <complex>
#include <numeric>
#include <functional>
#include <random>
#include <regex>
using namespace std;

typedef long long ll;typedef unsigned long long ull;typedef long double ld;

#define ALL(c) c.begin(),c.end()
#define IN(l,v,r) (l<=v && v < r)
template<class T> void UNIQUE(T v){v.erase(unique(ALL(v)),v.end());}
//debug
#define DUMP(x) cerr << #x <<" = " << (x)
#define LINE() cerr<< " (L" << __LINE__ << ")"

struct range{
    struct Iter{
        int v,step;
        Iter& operator++(){v+=step;return *this;}
        bool operator!=(Iter& itr){return v<itr.v;}
        int& operator*(){return v;}
    };
    Iter i, n;
    range(int i, int n,int step):i({i,step}), n({n,step}){}
    range(int i, int n):range(i,n,1){}
    range(int n):range(0,n){}
    Iter& begin(){return i;}
    Iter& end(){return n;}
};
struct rrange{
    struct Iter{
        int v,step;
        Iter& operator++(){v-=step;return *this;}
        bool operator!=(Iter& itr){return v>itr.v;}
        int& operator*(){return v;}
    };
    Iter i, n;
    rrange(int i, int n,int step):i({i-1,step}), n({n-1,step}){}
    rrange(int i, int n):rrange(i,n,1){}
    rrange(int n) :rrange(0,n){}
    Iter& begin(){return n;}
    Iter& end(){return i;}
};

//input
template<typename T1,typename T2> istream& operator >> (istream& is,pair<T1,T2>& p){return is>>p.first>>p.second;}
template<typename T1> istream& operator >> (istream& is,tuple<T1>& t){return is >> get<0>(t);}
template<typename T1,typename T2> istream& operator >> (istream& is,tuple<T1,T2>& t){return is >> get<0>(t) >> get<1>(t);}
template<typename T1,typename T2,typename T3> istream& operator >> (istream& is,tuple<T1,T2,T3>& t){return is >>get<0>(t)>>get<1>(t)>>get<2>(t);}
template<typename T1,typename T2,typename T3,typename T4> istream& operator >> (istream& is,tuple<T1,T2,T3,T4>& t){return is >> get<0>(t)>>get<1>(t)>>get<2>(t)>>get<3>(t);}
template<typename T> istream& operator >> (istream& is,vector<T>& as){for(int i:range(as.size()))is >>as[i];return is;}
//output
template<typename T> ostream& operator << (ostream& os, const set<T>& ss){for(auto a:ss){if(a!=ss.begin())os<<" "; os<<a;}return os;}
template<typename T1,typename T2> ostream& operator << (ostream& os, const pair<T1,T2>& p){return os<<p.first<<" "<<p.second;}
template<typename K,typename V> ostream& operator << (ostream& os, const map<K,V>& m){bool isF=true;for(auto& p:m){if(!isF)os<<endl;os<<p;isF=false;}return os;}
template<typename T1> ostream& operator << (ostream& os, const tuple<T1>& t){return os << get<0>(t);}
template<typename T1,typename T2> ostream& operator << (ostream& os, const tuple<T1,T2>& t){return os << get<0>(t)<<" "<<get<1>(t);}
template<typename T1,typename T2,typename T3> ostream& operator << (ostream& os, const tuple<T1,T2,T3>& t){return os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t);}
template<typename T1,typename T2,typename T3,typename T4> ostream& operator << (ostream& os, const tuple<T1,T2,T3,T4>& t){return os << get<0>(t)<<" "<<get<1>(t)<<" "<<get<2>(t)<<" "<<get<3>(t);}
template<typename T> ostream& operator << (ostream& os, const vector<T>& as){for(int i:range(as.size())){if(i!=0)os<<" "; os<<as[i];}return os;}
template<typename T> ostream& operator << (ostream& os, const vector<vector<T>>& as){for(int i:range(as.size())){if(i!=0)os<<endl; os<<as[i];}return os;}

// values
template<typename T> inline T INF(){assert(false);};
template<> inline int INF<int>(){return 1<<28;};
template<> inline ll INF<ll>(){return 1LL<<58;};
template<> inline double INF<double>(){return 1e16;};
template<> inline long double INF<long double>(){return 1e16;};

template<class T> inline T EPS(){assert(false);};
template<> inline int EPS<int>(){return 1;};
template<> inline ll EPS<ll>(){return 1LL;};
template<> inline double EPS<double>(){return 1e-8;};
template<> inline long double EPS<long double>(){return 1e-8;};

// min{2^r | n < 2^r}
template<typename T> T upper_pow2(T n){ T res=1;while(res<n)res<<=1;return res;}
// max{d | 2^d  <= n}
template<typename T> T msb(T n){ int d=62;while((1LL<<d)>n)d--;return d;}

template<typename T,typename U> T pmod(T v,U M){return (v%M+M)%M;}

ll gcd_positive(ll a,ll b) { return b == 0 ? a : gcd_positive(b,a%b); }
ll gcd(ll a,ll b) { return gcd_positive(abs(a), abs(b)); }
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}

namespace _double_tmpl{
    typedef long double D;
    
    static constexpr D Ae=0;
    D A(D a,D b){return a+b;}D Ainv(D a){return -a;}
    D S(D a,D b){return A(a,Ainv(b));}
    
    static constexpr D Me=1;
    D M(D a,D b){return a*b;}D Minv(D a){return 1.0/a;};

    int sig(D a,D b=0){return a<b-EPS<D>()?-1:a>b+EPS<D>()?1:0;}
    template<typename T> bool eq(const T& a,const T& b){return sig(abs(a-b))==0;}

    D pfmod(D v,D MOD=2*M_PI){return fmod(fmod(v,MOD)+MOD,MOD);}
    
    //[0,PI)
    D AbsArg(D a){
        D ret=pfmod(max(a,-a),2*M_PI);return min(ret,2*M_PI-ret);
    }
}
using namespace _double_tmpl;
// double PI=acos(-1);

typedef complex<D> P,Vec;
const P O=P(0,0);
#define X real()
#define Y imag()
istream& operator >> (istream& is,complex<D>& p){
    D x,y;is >> x >> y;p=P(x,y);return is;
}
bool compX (const P& a,const P& b){return !eq(a.X,b.X)?sig(a.X,b.X)<0:sig(a.Y,b.Y)<0;}
bool compY (const P& a,const P& b){return !eq(a.Y,b.Y)?sig(a.Y,b.Y)<0:sig(a.X,b.X)<0;}

// a×b
D cross(const Vec& a,const Vec& b){return imag(conj(a)*b);}
// a・b
D dot(const Vec&a,const Vec& b) {return real(conj(a)*b);}

int ccw(const P& a,P b,P c){
    b -= a; c -= a;
    if (sig(cross(b,c))>0)   return +1;       // counter clockwise
    if (sig(cross(b,c))<0)   return -1;       // clockwise
    if (sig(dot(b,c)) < 0)     return +2;       // c--a--b on line
    if (sig(norm(b),norm(c))<0) return -2;       // a--b--c on line
    return 0;
}

namespace std{
    bool operator < (const P& a,const P& b){return compX(a,b);}
    bool operator == (const P& a,const P& b){return eq(a,b);}
};

namespace _L{
    struct L : public vector<P> {
        P vec() const {return this->at(1)-this->at(0);}
        L(const P &a, const P &b){push_back(a); push_back(b);}
        L(){push_back(P(0,0));push_back(P(0,0));}
    };
    istream& operator >> (istream& is,L& l){P s,t;is >> s >> t;l=L(s,t);return is;}

    bool isIntersectLL(const L &l, const L &m) {
        return sig(cross(l.vec(), m.vec()))!=0 || // non-parallel
        sig(cross(l.vec(), m[0]-l[0])) ==0;   // same line
    }
    bool isIntersectLS(const L &l, const L &s) {
      return sig(cross(l.vec(), s[0]-l[0])*       // s[0] is left of l
             cross(l.vec(), s[1]-l[0]))<=0; // s[1] is right of l
    }
    bool isIntersectLP(const L &l, const P &p) {
        return sig(cross(l[1]-p, l[0]-p))==0;
    }

    // verified by ACAC003 B
    // http://judge.u-aizu.ac.jp/onlinejudge/creview.jsp?rid=899178&cid=ACAC003
    bool isIntersectSS(const L &s, const L &t) {
      return ccw(s[0],s[1],t[0])*ccw(s[0],s[1],t[1]) <= 0 &&
             ccw(t[0],t[1],s[0])*ccw(t[0],t[1],s[1]) <= 0;
    }
    bool isIntersectSP(const L &s, const P &p) {
      return sig(abs(s[0]-p)+abs(s[1]-p),abs(s[1]-s[0])) <=0; // triangle inequality
    }

    // 直線へ射影した時の点
    // verified by AOJLIB
    // http://judge.u-aizu.ac.jp/onlinejudge/review.jsp?rid=1092212
    P projection(const L &l, const P &p) {
      D t = dot(p-l[0],l.vec()) / norm(l.vec());
      return l[0] + t * l.vec();
    }
    //対称な点
    // verified by AOJLIB
    // http://judge.u-aizu.ac.jp/onlinejudge/review.jsp?rid=1092214
    P reflection(const L &l, const P &p) {
      return p + 2.0L * (projection(l, p) - p);
    }
    D distanceLP(const L &l, const P &p) {
      return abs(p - projection(l, p));
    }
    D distanceLL(const L &l, const L &m) {
      return isIntersectLL(l, m) ? 0 : distanceLP(l, m[0]);
    }
    D distanceLS(const L &l, const L &s) {
        if (isIntersectLS(l, s)) return 0;
        return min(distanceLP(l, s[0]), distanceLP(l, s[1]));
    }
    D distanceSP(const L &s, const P &p) {
      const P r = projection(s, p);
      if (isIntersectSP(s, r)) return abs(r - p);
      return min(abs(s[0] - p), abs(s[1] - p));
    }
    D distanceSS(const L &s, const L &t) {
        if (isIntersectSS(s, t)) return 0;
        return min(min(distanceSP(s, t[0]), distanceSP(s, t[1])),
                 min(distanceSP(t, s[0]), distanceSP(t, s[1])));
    }

    // 交点計算
    // verified by AOJLIB
    // http://judge.u-aizu.ac.jp/onlinejudge/review.jsp?rid=1092231
    P crosspoint(const L &l, const L &m) {
      D A = cross(l.vec(), m.vec()),B = cross(l.vec(), l[1] - m[0]);
      if (sig(A)==0 && sig(B)==0) return m[0]; // same line
      assert(sig(A)!=0);//err -> 交点を持たない．
      return m[0] + B / A * (m[1] - m[0]);
    }
}
using namespace _L;

class Main{
    public:

    void run(){
        P a,b;cin >> a >> b; b = P(-b.X,b.Y);
        L l(a,b),l0(P(0,0),P(0,1));
        cout << crosspoint(l,l0).Y << endl;
    }
};

int main(){
    cout <<fixed<<setprecision(20);
    cin.tie(0);
    ios::sync_with_stdio(false);
    Main().run();
    return 0;
}