#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#define INF 1000000000#define MAXN 40using namespace std;double dp[1 << 10][MAXN];int d[MAXN][MAXN];int t[MAXN];int n, m, p, a, b;void solve(){for (int i = 0; i<(1 << n); i++)fill(dp[i], dp[i] + m, INF);dp[(1 << n) - 1][a-1] = 0;double res = INF;for (int s = (1 << n) - 1; s >= 0; s--){res = min(res, dp[s][b - 1]);for (int v = 0; v < m; v++)for (int i = 0; i < n; i++){if (s >> i & 1){for (int u = 0; u < m; u++)if (d[v][u] >= 0)dp[s&~(1 << i)][u] = min(dp[s&~(1 << i)][u], dp[s][v] + (double)d[v][u] / t[i]);}}}if (res == INF)cout << "Impossible" << endl;elseprintf("%.3fn", res);}int main(){int x, y, z;while (cin >> n >> m >> p >> a >> b&&n || m || p || a || b){for (int i = 0; i < n; i++)cin >> t[i];memset(d, -1, sizeof(d));for (int i = 1; i <= p; i++){cin >> x >> y >> z;d[x-1][y-1] = d[y-1][x-1] = z;}solve();}return 0;}
