HDOJ 2001

 //如果把x1,x2,y1,y2定义为int，则会报Output Limit Exceeded的错误！  

#include "stdio.h"
#include "math.h"

int main(void){
	double x1, x2, y1, y2;
	double csum;
	double distance;	//距离
	
	while(scanf("%lf%lf%lf%lf", &x1, &y1, &x2, &y2) != EOF){
		csum = (double)(x2-x1)*(x2-x1) + (y2-y1)*(y2-y1);
		distance = sqrt(csum);
		
		printf("%.2lf\n", distance);
		
		csum = 0.00;
		distance = 0.00;
	} 
	
	return 0;
}