```cpp

include[HTML_REMOVED]

include[HTML_REMOVED]

int main(){
double x1,x2,y1,y2,d;
scanf(“%lf %lf\n”,&x1,&y1);
scanf(“%lf %lf”,&x2,&y2);
d=sqrt((x1-x2)(x1-x2)+(y1-y2)(y1-y2));
printf(“%.4lf”,d);//检查冒号
return 0;
}