/*
枚举所有情况，通过并查集判断在当前情况下，是否包含起始和终止点，
若包含，则需判断是否在当前情况下，最大速度和最小速度的比更小，
若是，则更新最大速度和最小速度。
最后枚举过所有情况后，即获得答案。
*/
1 #include <iostream>
2 #include <cstdlib>
3 #include <cstdio>
4 #include <cstddef>
5 #include <iterator>
6 #include <algorithm>
7 #include <string>
8 #include <locale>
9 #include <cmath>
10 #include <vector>
11 #include <cstring>
12 #include <map>
13 #include <utility>
14 #include <queue>
15 #include <stack>
16 #include <set>
17 #include <functional>
18 using namespace std;
19 typedef pair<int, int> P;
20 const int INF = 0x3f3f3f3f;
21 const int modPrime = 3046721;
22 const double eps = 1e-9;
23 const int MaxN = 505;
24 const int MaxM = 5005;
25
26
27 int N, M, s, t;
28 string exampleNum;
29
30 struct Node
31 {
32 int x, y, v;
33 };
34
35 Node nodeVec[MaxM];
36
37 bool Cmp(const Node n1, const Node n2)
38 {
39 return n1.v < n2.v;
40 }
41
42
43 int gcd(int a, int b)
44 {
45 if (b == 0) return a;
46 else gcd(b, a%b);
47 }
48
49
50 ///////////////////////////////////
51 //并查集(Union-Find Sets)
52 int ifather[MaxN];
53 int irank[MaxN];
54
55 void ufsinit(int n)
56 {
57 for (int i = 0; i <= n; ++i)
58 {
59 ifather[i] = i;
60 irank[i] = 0;
61 }
62 }
63
64 int ufsFind(int x)
65 {
66 if (ifather[x] == x)
67 {
68 return x;
69 }
70 else
71 {
72 return ifather[x] = ufsFind(ifather[x]);
73 }
74 }
75
76 void ufsUnite(int x, int y)
77 {
78 x = ufsFind(x);
79 y = ufsFind(y);
80
81 if (x == y)
82 {
83 return;
84 }
85
86 if (irank[x] < irank[y])
87 {
88 ifather[x] = y;
89 }
90 else
91 {
92 ifather[y] = x;
93 if (irank[x] == irank[y])
94 {
95 ++irank[x];
96 }
97 }
98 }
99
100 ///////////////////////////////////
101
102 void Solve()
103 {
104 int ansMax = INF;
105 int ansMin = 1;
106 bool havePath = false;
107 for (int i = 0; i < M; ++i)
108 {
109 ufsinit(N);
110 for (int j = i; j >= 0; --j)
111 {
112 ufsUnite(nodeVec[j].x, nodeVec[j].y);
113 if (ufsFind(s) == ufsFind(t))
114 {
115 if ((ansMax*1.0 / ansMin) - (nodeVec[i].v*1.0 / nodeVec[j].v) > eps)
116 {
117 ansMax = nodeVec[i].v;
118 ansMin = nodeVec[j].v;
119 if (!havePath)
120 {
121 havePath = true;
122 }
123 }
124 break;
125 }
126 }
127 }
128 if (!havePath)
129 {
130 printf("IMPOSSIBLE
");
131 }
132 else
133 {
134 int iGcd = gcd(ansMax, ansMin);
135 ansMax /= iGcd;
136 ansMin /= iGcd;
137 if (ansMin == 1)
138 {
139 printf("%d
", ansMax);
140 }
141 else
142 {
143 printf("%d/%d
", ansMax, ansMin);
144 }
145 }
146 }
147
148 int main()
149 {
150 #ifdef HOME
151 freopen("in", "r", stdin);
152 //freopen("out", "w", stdout);
153 #endif
154
155 while (~scanf("%d %d", &N, &M))
156 {
157 Node nd;
158 for (int i = 0; i < M; ++i)
159 {
160 scanf("%d %d %d", &nd.x, &nd.y, &nd.v);
161 nodeVec[i] = nd;
162 }
163 sort(nodeVec, nodeVec + M, Cmp);
164 scanf("%d %d", &s, &t);
165 Solve();
166 }
167
168 #ifdef HOME
169 cerr << "Time elapsed: " << clock() / CLOCKS_PER_SEC << " ms" << endl;
170 _CrtDumpMemoryLeaks();
171 #endif
172 return 0;
173 }