include[HTML_REMOVED]
include[HTML_REMOVED]
include[HTML_REMOVED]
using namespace std;
int main(){
double x1,y1,x2,y2;
cin >> x1 >> y1;
cin >> x2 >> y2;
printf("%.4lf",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)));
//printf("%.4lf",sqrt(pow(x1-x2,2)+pow(y1-y2,2)));
return 0;
}