int main(){
float x1,y1,x2,y2;
scanf("%f %f %f %f",&x1,&y1,&x2,&y2); printf("%f\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
return(0); }
int main(){
float x1,y1,x2,y2;
scanf("%f %f %f %f",&x1,&y1,&x2,&y2); printf("%f\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
return(0); }