#include<iostream>
#include<cmath>
using namespace std;

class CPoint{
  public:
        double x;
        double y;
      //  CPoint(){}
        CPoint(int x1,int y1){
          x = x1;
          y = y1;
        }
        double operator -(CPoint & A)const{
          return sqrt(pow(x - A.x ,2) + pow(y - A.y , 2));
        }
};

int main (){
  int x1 , x2, y1, y2;
  cout <<"请依次输入两点坐标："<<endl;
  cin >> x1 >>y1 >>x2 >>y2;
  CPoint p1(x1 , y1), p2( x2, y2);
  cout <<"两点距离：" <<p1-p2<<endl;
  return 0;
}