s1=input() s2=input() x1=float(s1.split(' ',2)[0]) y1=float(s1.split(' ',2)[1]) x2=float(s2.split(' ',2)[0]) y2=float(s2.split(' ',2)[1]) print("%.4f" %(((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1))**0.5))