uses crt;
const fi='baitap.txt'
var f1:text;
a,b,c,d:array[1..100]of real;
i,n:integer;
begin
clrscr;
assign(f1,fi); reset(f1);
n:=0;
while not eof(f1) do
begin
n:=n+1;
readln(f1,a[n],b[n],c[n],d[n]);
end;
for i:=1 to n do
writeln(sqrt(sqr(a[i]-c[i])+sqr(b[i]-d[i])):4:3);
close(f1);
readln;
end.