#include<cstdio> #include<cmath> int main() { double x1,x2,y1,y2; scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2); printf("%.4lf\n",sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2))); return 0; }
