#include <iostream>#include <cstdlib>#include <cstdio>#include <cstring>using namespace std;#define maxn 505#define maxm maxn * maxn#define inf 0x3f3f3f3fstruct Edge{ int v, w, next;}edge[maxm];int n, m;int head[maxn];int edge_num;int q[maxn];int dist[maxn];bool vis[maxn];void addedge(int a, int b, int w){ edge[edge_num].v = b; edge[edge_num].w = w; edge[edge_num].next = head[a]; head[a] = edge_num++;}void input(){ memset(head, -1, sizeof(head)); edge_num = 0; for (int i = 0; i < m; i++) { int a, b, w; scanf("%d%d%d", &a, &b, &w); a--; b--; addedge(a, b, w); addedge(b, a, w); }}bool relax(int u, Edge &e){ if (dist[e.v] > dist[u] + e.w) { dist[e.v] = dist[u] + e.w; return true; } return false;}bool spfa(int x){ memset(vis, 0, sizeof(vis)); for (int i = 0; i < n; i++) dist[i] = inf; int front = 0; int rear = 1; q[front] = x; dist[x] = 0; vis[x] = true; while (front != rear) { int temp = q[front++]; if (front == maxn) front = 0; vis[temp] = false; for (int i = head[temp]; i != -1; i = edge[i].next) { if (relax(temp, edge[i]) && !vis[edge[i].v]) { q[rear++] = edge[i].v; if (rear == maxn) rear = 0; } } } return false;}double get_time(int a, int b, int w){ if (a > b) swap(a, b); if (a + w <= b) return b; return b + (w - (b - a)) * 1.0 / 2;}void work(){ int ans = 0; for (int i = 0; i < n; i++) if (dist[ans] < dist[i]) ans = i; int a, b; double max_time; max_time = dist[ans]; for (int u = 0; u < n; u++) for (int i = head[u]; ~i; i = edge[i].next) { int v = edge[i].v; double temp = get_time(dist[u], dist[v], edge[i].w); if (temp > max_time) { a = min(u, v); b = max(u, v); max_time = temp; } } if (max_time > dist[ans]) printf("The last domino falls after %.1f seconds, between key dominoes %d and %d.n", max_time, a + 1, b + 1); else printf("The last domino falls after %.1f seconds, at key domino %d.n", (double)dist[ans], ans + 1);}int main(){ int t = 0; while (scanf("%d%d", &n, &m), n | m) { printf("System #%dn", ++t); input(); spfa(0); work(); puts(""); } return 0;}
