#include <iostream>
#include <cstdlib>
#include <cmath>

using namespace std;

double typ_apokl(double,double,double,double,double);
double mo(double,double,double,double);

int main()
{
	double s1,s2,s3,s4,a;
	do{
		cout<<"grapse tis 4 bathmologies h dwse enan arnhtiko gia termatismo"<<endl;
		cin>>s1;
		if (s1>=0)//an dwsei arnhtiko prospernaei oti yparxeisthn if kai termatizetai kai h while//
		{
		    cin>>s2>>s3>>s4;
		    a=mo(s1,s2,s3,s4);
		    cout<<"h typikh apoklish twn 4 ari8mwn einai "<<typ_apokl(s1,s2,s3,s4,a)<<endl;
	    }
	}while (s1>=0);
	
	
	system ("PAUSE");
	return 0;	
}
double typ_apokl(double s1, double s2, double s3, double s4,double a)
{
	return sqrt(pow(s1-a,2)+pow(s2-a,2)+pow(s3-a,2)+pow(s4-a,2));
}
double mo(double s1, double s2, double s3, double s4)
{
	if (s1+s2+s3+s4!=0) return (s1+s2+s3+s4)/4;
	if (s1+s2+s3+s4==0) return 0;
}