1015.c

#include<stdio.h>

#include<math.h>

 

int main()

{

    double x1, y1, x2, y2, p1, p2, distance;

    scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);

    p1 = x2 - x1;

    p2= y2 - y1;

    distance = sqrt((p1 * p1) + (p2 * p2));

    printf("%.4lf\n", distance);

    return 0;

}