#include <stdio.h>
#include<math.h>
int main(void){
    int x1, x2, y1, y2, z;
    scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);
    z = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
    printf("%.8lf\n", z);
    
    return (0);
}
