1 type
2 arr=record
3 y,next:longint;
4 w:real;
5 end;
6 var
7 bo:boolean;
8 n,m,nm:longint;
9 a:array [0..10001] of arr;
10 d:array [0..3001] of real;
11 ls,v:array [0..3001] of longint;
12 procedure add(x,y:longint;z:real);
13 begin
14 inc(nm);
15 a[nm].y:=y; a[nm].w:=z;
16 a[nm].next:=ls[x]; ls[x]:=nm;
17 end;
18
19 procedure init;
20 var
21 i,x,y:longint;
22 z:real;
23 begin
24 readln(n,m);
25 nm:=0;
26 for i:=1 to m do
27 begin
28 readln(x,y,z);
29 add(x,y,z);
30 end;
31 end;
32
33 procedure dfs(x:longint;mid:real);
34 var
35 i:longint;
36 begin
37 v[x]:=1; i:=ls[x];
38 while i<>0 do
39 with a[i] do
40 begin
41 if d[x]+w-mid<d[y] then
42 begin
43 if v[y]=1 then
44 begin
45 bo:=true;
46 exit;
47 end;
48 d[y]:=d[x]+w-mid;
49 dfs(y,mid);
50 if bo then exit;
51 end;
52 i:=next;
53 end;
54 v[x]:=0;
55 end;
56
57 function pd(mid:real):boolean;
58 var
59 i:longint;
60 begin
61 for i:=1 to n do
62 begin
63 d[i]:=0; v[i]:=0;
64 end;
65 for i:=1 to n do
66 begin
67 bo:=false;
68 dfs(i,mid);
69 if bo then exit(true);
70 end;
71 exit(false);
72 end;
73
74 procedure main;
75 var
76 l,r,mid:real;
77 begin
78 l:=-100000; r:=100000;
79 while r-l>=0.0000001 do
80 begin
81 mid:=(l+r)/2;
82 if pd(mid) then r:=mid
83 else l:=mid;
84 end;
85 writeln(mid:0:6);
86 end;
87
88 begin
89 init;
90 main;
91 end.
