Problem: There is a forest that we model as a plane and live n rare animals. Animal number i has its lair in the point (x_{i}, y_{i}). In order to protect them, a decision to build a nature reserve has been made.

The reserve must have a form of a circle containing all lairs. There is also a straight river flowing through the forest. All animals drink from this river, therefore it must have at least one common point with the reserve. On the other hand, ships constantly sail along the river, so the reserve must not have more than one common point with the river.

For convenience, scientists have made a transformation of coordinates so that the river is defined by y = 0. Check whether it is possible to build a reserve, and if possible, find the minimum possible radius of such a reserve.

Input

The first line contains one integer n (1 ≤ n ≤ 10^5) — the number of animals. 

Each of the next n lines contains two integers x_{i}, y_{i} (-10^7 ≤ x_{i}, y_{i} ≤ 10^7) — the coordinates of the i-th animal's lair. It is guaranteed that y_{i} ≠ 0. No two lairs coincide.

Output

If the reserve cannot be built, print -1. Otherwise print the minimum radius. Your answer will be accepted if absolute or relative error does not exceed 10^{-6}.

Formally, let your answer be a, and the jury's answer be b. Your answer is considered correct if \frac{|a - b|}{max{(1, |b|)}} ≤ 10^{-6}.

Examples

Input

1
0 1


Output

0.5

Input

3
0 1
0 2
0 -3


Output

-1


Input

2
0 1
1 1


Output

0.625

Note

In the first sample it is optimal to build the reserve with the radius equal to 0.5 and the center in (0,\ 0.5).

In the second sample it is impossible to build a reserve.

In the third sample it is optimal to build the reserve with the radius equal to 5/8 and the center in (1/2,\ 5/8).

Solution (in JAVA):

Solution:
import java.io.*;
import java.util.*;
public class Taska{
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskE solver = new TaskE();
        solver.solve(1, in, out);
        out.flush();out.close();
    }
        static class TaskE {
        class pair{
        	double x,y;
        	pair(double a,double b){x=a;y=b;}
        }
        pair p[];int n;
        double min=Long.MIN_VALUE,max=Long.MAX_VALUE;
        double pmin,pmax;
        boolean verify(double r){
        	pmin=min;pmax=max;
        	for(int i=0;i<n;i++){
        		if(2*r<p[i].x)return false;
        		double val=2*r*p[i].x-p[i].x*p[i].x;
        		double add=Math.sqrt(val);
        		double ymin=p[i].y-add,ymax=p[i].y+add;
        		if(!chk(ymin,ymax))return false;
        	}return true;
        }
        boolean chk(double ymin,double ymax){
        	if(ymin>pmax||ymax<pmin)return false;
        	pmax=Math.min(pmax,ymax);
        	pmin=Math.max(pmin,ymin);
        	if(pmin>pmax)return false;
        	return true;
        }
	 	  public void solve(int testNumber, InputReader in, PrintWriter out) {
 			n=in.nextInt();
 			p=new pair[n];
 			boolean isn=false,isp=false;
 			for(int i=0;i<n;i++){
 				double x=in.nextDouble(),y=in.nextDouble();
 				p[i]=new pair(y,x);
 				if(p[i].x<0)isn=true;
 				if(p[i].x>0)isp=true;
 				p[i].x=Math.abs(p[i].x);
 			}
 			if(isn&&isp){
 				out.print("-1");return;
 			}
 			if(n==1){
 				out.print(p[0].x/2);return;
 			}
 			int it=100;
 			double l=0,r=(long)1E18;
 			double ans=-1;
 			for(int i=0;i<=it;i++){
 				double m=(l+r)/2;
 				if(verify(m)){
 					ans=m;r=m;
 				}else l=m;
 			}
 			out.print(ans);
          }
//         pair ja[][];long w[];int from[],to[],c[];
//             void make(int n,int m,InputReader in){
//              ja=new pair[n+1][];w=new long[m];from=new int[m];to=new int[m];c=new int[n+1];
//              for(int i=0;i<m;i++){
//               int u=in.nextInt(),v=in.nextInt();long wt=in.nextLong();
//               c[u]++;c[v]++;from[i]=u;to[i]=v;w[i]=wt;
//              }
//              for(int i=1;i<=n;i++){
//               ja[i]=new pair[c[i]];c[i]=0;
//              }
//              for(int i=0;i<m;i++){
//               ja[from[i]][c[from[i]]++]=new pair(to[i],w[i]);
//               ja[to[i]][c[to[i]]++]=new pair(from[i],w[i]);
//              }
//             }
//        int[] radixSort(int[] f){ return radixSort(f, f.length); }
//	int[] radixSort(int[] f, int n)
//	{
//		int[] to = new int[n];
//		{
//			int[] b = new int[65537];
//			for(int i = 0;i < n;i++)b[1+(f[i]&0xffff)]++;
//			for(int i = 1;i <= 65536;i++)b[i]+=b[i-1];
//			for(int i = 0;i < n;i++)to[b[f[i]&0xffff]++] = f[i];
//			int[] d = f; f = to;to = d;
//		}
//		{
//			int[] b = new int[65537];
//			for(int i = 0;i < n;i++)b[1+(f[i]>>>16)]++;
//			for(int i = 1;i <= 65536;i++)b[i]+=b[i-1];
//			for(int i = 0;i < n;i++)to[b[f[i]>>>16]++] = f[i];
//			int[] d = f; f = to;to = d;
//		}
//		return f;
//	}
    }
    static class InputReader {
        BufferedReader br;
        StringTokenizer st;
        public InputReader(InputStream stream) {
            br = new BufferedReader(new InputStreamReader(stream));
            st = null;
        }

        String next() {
            while (st == null || !st.hasMoreTokens()) {
                String s = null;
                try {
                    s = br.readLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (s == null)
                    return null;
                st = new StringTokenizer(s);
            }
            return st.nextToken();
        }

        boolean hasMoreTokens() {
            while (st == null || !st.hasMoreTokens()) {
                String s = null;
                try {
                    s = br.readLine();
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (s == null)
                    return false;
                st = new StringTokenizer(s);
            }
            return true;
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }
        public long nextLong() {
            return Long.parseLong(next());
        }
        public double nextDouble() {
            return Double.parseDouble(next());
        }
    }
}