program Zada4a_2;

{$APPTYPE CONSOLE}
var
x1,x2,y1,y2,L:real;
begin
write('x1='); readln(x1);
write('x2='); readln(x2);
write('y1='); readln(y1);
write('y2='); readln(y2);
L:=SQRT((SQR(x2-x1))+(SQR(y2-y1)));
write('L=',L:6:2);
readln;
end.