不会的看我！！！

#include <bits/stdc++.h>
using namespace std;
int main()
{
	double x1,x2,y1,y2,dis;
	cin>>x1>>y1>>x2>>y2;
	
	dis = sqrt((x2-x1)*(x2-x1) + (y2-y1)*(y2-y1));
	printf("%.2f",dis);

	return 0;
}