#include <stdio.h>
#include <math.h>

struct point {
  double x;
  double y;
};

double dist(struct point p1, struct point p2){
  double result;
  result = sqrt((p2.x - p1.x)*(p2.x - p1.x) +
		(p2.y - p1.y)*(p2.y - p1.y));
  return result;
}

int main(void){
  struct point point_a = {1.0, 2.0};
  struct point point_b = {4.0, 6.0};

  double d;

  d = dist(point_a, point_b);
  printf("%lf\n", d);

  return(0);
}