#include <cstdio>#include <cstring>#include <algorithm>#include <climits>#include <string>#include <iostream>#include <map>#include <cstdlib>#include <list>#include <set>#include <queue>#include <stack>using namespace std;int n,m;const int maxn=505;struct Node{    int x;int val;}node[maxn];struct cmp{    bool operator ()(const Node &a,const Node &b)    {        return a.val<b.val;    }};const int INF=10000000;int dis[maxn];int vis[maxn];int Map[maxn][maxn];void djs(int x){    for(int i=1;i<=n;i++){        dis[i]=INF;vis[i]=0;    }    dis[x]=0;vis[x]=1;    Node k; k.x=x;k.val=0;    priority_queue<Node,vector<Node> ,cmp> q;    q.push(k);    while(!q.empty()){        Node k=q.top();q.pop(); int cur=k.x;vis[x]=1;        for(int i=1;i<=n;i++){            if(dis[i]>dis[cur]+Map[cur][i]){                dis[i]=dis[cur]+Map[cur][i];                if(!vis[i]){                    Node k; k.x=i;k.val=dis[i];                    q.push(k);                }            }        }    }}int main(){    int ret=0;    while(cin>>n>>m,++ret&&n||m){        for(int i=1;i<=n;i++)            for(int j=1;j<=n;j++)            Map[i][j]=INF;        for(int i=0;i<m;i++){            int a,b,c;cin>>a>>b>>c;            if(Map[a][b]>c) Map[a][b]=Map[b][a]=c;        }        djs(1);        double ans=0;int sign=1;        for(int i=1;i<=n;i++)        if(dis[i]>ans){            ans=dis[i];sign=i;        }        double ans1=0;int a;int b;        for(int i=1;i<=n;i++){            for(int j=i+1;j<=n;j++)if(Map[i][j]!=INF) {                double t=(dis[i]+dis[j]+Map[i][j])/2.0;                if(t>ans1) {                    ans1=t; a=i;b=j;                }            }        }      //  for(int i=1;i<=n;i++)          //  cout<<dis[i]<<endl;        if(ret!=1) cout<<endl;        printf("System #%d\n",ret);        if(ans1>ans){            printf("The last domino falls after %.1f seconds, between key dominoes %d and %d.\n",ans1,a,b);        }        else{            printf("The last domino falls after %.1f seconds, at key domino %d.\n",ans,sign);        }    }    return 0;}