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.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.Arrays;

public class D {

	static int N;
	static Vector ar[];
	public static void main(String[] args) {
		JS in = new JS();
		N = in.nextInt();
		boolean pos = false;
		boolean neg = false;
		int onZero = 0;
		double zeroX = -1;
		ar = new Vector[N];
		for(int i = 0; i < N; i++) {
			ar[i] = new Vector(in.nextDouble(),in.nextDouble());
			if(ar[i].y > 0) pos=true;
			if(ar[i].y < 0) neg=true;
			if(ar[i].y < 0) ar[i].y = ar[i].y*-1;
			if(ar[i].y==0) {
				onZero++;
				zeroX = ar[i].x;
			}
		}
		if((pos&&neg)||onZero > 1) {
			System.out.println(-1);
			return;
		}
		Arrays.sort(ar);
		if(onZero == 1) {
			System.out.println(eval(zeroX));
		}
		else {
			double rad = tern(-100000000,100000000, 200);
			System.out.println(rad);
		}
	}
	static double tern(double lo, double hi, int iter) {
		if(iter==0)return eval(lo);
		double lt = lo + (hi-lo)/3.;
		double rt = lo + 2.*(hi-lo)/3.;
		double lVal = eval(lt);
		double rVal = eval(rt);
		if(lVal < rVal) return tern(lo,rt,iter-1);
		else return tern(lt,hi,iter-1);
	}
	static double eval(double xPos) {
		//get the radius for this position
		//System.out.println("X="+xPos);
		double curR = 0;
		for(int i = 0; i < N; i++) {
			if(ar[i].y==0)continue;
			double r = -1;
			double val = xPos*xPos - 2*xPos*ar[i].x + ar[i].x*ar[i].x + ar[i].y*ar[i].y;
			val = val / (2*ar[i].y);
			r = val;
			curR = Math.max(curR, r);
		}
		return curR;
	}
	
	static class Vector implements Comparable<Vector>{
		double x,y;
		public Vector(double xx, double yy) {
			x=xx;
			y=yy;
		}
		@Override
		public int compareTo(Vector o) {
			if(x < o.x) return -1;
			if(x > o.x) return 1;
			if(y < o.y) return -1;
			if(y > o.y) return 1;
			return 0;
		}
	}

	
	static class JS{
		public int BS = 1<<16;
		public char NC = (char)0;
		byte[] buf = new byte[BS];
		int bId = 0, size = 0;
		char c = NC;
		double num = 1;
		BufferedInputStream in;
		
		public JS() {
			in = new BufferedInputStream(System.in, BS);
		}
		
		public JS(String s) throws FileNotFoundException {
			in = new BufferedInputStream(new FileInputStream(new File(s)), BS);
		}
		
		public char nextChar(){
			while(bId==size) {
				try {
					size = in.read(buf);
				}catch(Exception e) {
					return NC;
				}				
				if(size==-1)return NC;
				bId=0;
			}
			return (char)buf[bId++];
		}
		
		public int nextInt() {
			return (int)nextLong();
		}
		
		public long nextLong() {
			num=1;
			boolean neg = false;
			if(c==NC)c=nextChar();
			for(;(c<'0' || c>'9'); c = nextChar()) {
				if(c=='-')neg=true;
			}
			long res = 0;
			for(; c>='0' && c <='9'; c=nextChar()) {
				res = (res<<3)+(res<<1)+c-'0';
				num*=10;
			}
			return neg?-res:res;
		}
		
		public double nextDouble() {
		    while(c!='.'&&c!='-'&&(c <'0' || c>'9')) c = nextChar();
		    boolean neg = c=='-';
		    if(neg)c=nextChar();
		    boolean fl = c=='.';
		    double cur = nextLong();
		    if(fl) return neg ? -cur/num : cur/num;
		    if(c == '.') {
			double next = nextLong();
			return neg ? -cur-next/num : cur+next/num;
		    }
		    else return neg ? -cur : cur;
		}
		
		public String next() {
			StringBuilder res = new StringBuilder();
			while(c<=32)c=nextChar();
			while(c>32) {
				res.append(c);
				c=nextChar();
			}
			return res.toString();
		}
		
		public String nextLine() {
			StringBuilder res = new StringBuilder();
			while(c<=32)c=nextChar();
			while(c!='\n') {
				res.append(c);
				c=nextChar();
			}
			return res.toString();
		}

		public boolean hasNext() {
			if(c>32)return true;
			while(true) {
				c=nextChar();
				if(c==NC)return false;
				else if(c>32)return true;
			}
		}
	}
	
}