#include
#include
using namespace std;
typedef struct Point
{
double x;
double y;
}Point;
double Distance(Point p1, Point p2)
{
return sqrt(pow((p1.x - p2.x), 2) + pow((p1.y - p2.y), 2));
//俩点距离是这么求的!
}
int main()
{
Point p1, p2;
cin >> p1.x >> p1.y >> p2.x >> p2.y;
cout << "distance: " << Distance(p1, p2) << endl;
return 0;
}