#include <iostream>
#include <stdio.h>
using namespace std;

int MIN(int a, int b){
	return a>b ? b : a;
}

int MAX(int a, int b){
	return a>b ? a : b;
}

int main() {
	int N,M, cnt = 0;
	while(1){
		cnt ++;
		scanf("%d%d", &N, &M);
		if(N == 0 && M == 0) return 0;
		printf("System #%d\n", cnt);
		if(N == 1){
			printf("The last domino falls after 0.0 seconds, at key domino 1.\n\n");
			continue;
		}
		int edges[502][502];
		for(int i = 1; i <= N; i++){
			for(int j = 1; j <= N; j++){
				edges[i][j] = -1;
				//-1表示不连
			}
		}
		for(int i = 0; i < M; i++){
			int I, J, L;
			scanf("%d%d%d", &I, &J, &L);
			edges[I][J] = L;
			edges[J][I] = L;
		}
		//开始dijkstra
		int dist[502];
		dist[1] = 0;
		for(int i = 2; i <= N; i++) dist[i] = 2147483647;
		bool in[502] = {0};
		int numCnt = N;
		while(numCnt > 0){
			int min = 2147483647;
			int arg = -1;
			for(int i = 1; i <= N; i++){
				if(in[i]) continue;
				if(dist[i] < min){
					min = dist[i];
					arg = i;
				}
			}
			dist[arg] = min;
			in[arg] = true;
			numCnt --;
			for(int i = 1; i <= N; i++){
				if(in[i]) continue;
				if(edges[arg][i] == -1) continue;
				if(min + edges[arg][i] < dist[i]){
					dist[i] = min + edges[arg][i];
				}
			}
		}
		double mx = 0;
		int argmax = 1;
		for(int i = 2; i <= N; i++){
			if(dist[i] > mx){
				mx = dist[i];
				argmax = i;
			}
		}
		double maxz = 0;
		int arg1 = -1, arg2 = -1;
		for(int i = 1; i <= N; i++){
			for(int j = 1; j <= N; j++){
				if(edges[i][j] == -1) continue;
				double temp = (dist[i] + dist[j] + edges[i][j])/2.0;
				if(temp > maxz){
					maxz = temp;
					arg1 = MIN(i,j);
					arg2 = MAX(i,j);
				}
			}
		}
		if(mx >= maxz){
			printf("The last domino falls after %.1lf seconds, at key domino %d.\n\n", mx, argmax);
		}
		else{
			printf("The last domino falls after %.1lf seconds, between key dominoes %d and %d.\n\n", maxz, arg1, arg2);
		}
	}
	return 0;
}