{思路分析：此题可以应用PRIM算法解决，关键是根据输入文件算出图的邻接矩阵，然后可以直接应用PRIM算法。}
program network;
const
  vmax=100;
var
    w:array[1..vmax,1..vmax]of real;
    x,y:array[1..vmax] of real;
    i,j,k,v,e:integer;
    sum:real;
procedure prim(v0:integer);
  var
    flag:array[1..vmax] of boolean;
    min:real;
    prevk,nextk:integer;
  begin
    fillchar(flag,sizeof(flag),false);
    flag[v0]:=true;
    for i:=1 to v-1 do
      begin
        min:=1e38;
        for k:=1 to v do
          if flag[k] then
             for j:=1 to v do
                if (not flag[j]) and (w[k,j]<min) and (w[k,j]<>0)
                 then begin
                     min:=w[k,j];
                     nextk:=j;
                     prevk:=k;
                   end;
         if min<>1e10
            then begin
                   flag[nextk]:=true;
                   {writeln(prevk,' ',nextk,' ',min:0:2);    此部分输出每个结点对的距离，因题目不要求所以不输出。}
                   sum:=sum+min;
                 end;
      end;
  end;{prim}
begin
  assign(input,'network.in');
  reset(input);
  assign(output,'network.out');
  rewrite(output);
  fillchar(w,sizeof(w),0);
  readln(v);
  for i:=1 to v do
    readln(x[i],y[i]);
  for i:=1 to v do                                           {计算图的邻接矩阵}
    begin
    for j:=i+1 to v do
       begin
         w[i,j]:=sqrt(sqr(x[i]-x[j])+sqr(y[i]-y[j]));
         w[j,i]:=w[i,j];
       end;
    end;
   sum:=0;
    prim(1);
    writeln(sum:0:2);
  close(input);
  close(output);
end.
//delphi/7191