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

float dist(float x1, float y1, float x2, float y2){
    return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
int main(){
    float x1,y1,x2,y2;

    scanf("%f %f %f %f",&x1,&y1,&x2,&y2);
    printf("%.2f\n", dist(x1,y1,x2,y2));
    return 0;
}