#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#define INF 1000.0#define V 105using namespace std;int num[V][V],n,N,m,i,x,y,j,p,k,zz;double R[V][V],map[V][V][V],ans[V],s[V],f[V][V],max,z,A,Max,temp;int main(){ while (scanf("%d%d",&n,&m)!=EOF) { memset(R,0,sizeof(R)); memset(s,0,sizeof(s)); memset(ans,0,sizeof(ans)); memset(num,0,sizeof(num)); memset(map,0,sizeof(map)); memset(f,0,sizeof(f)); A=0; for (i=1;i<=m;i++) scanf("%d%d%d",&x,&y,&zz),z=(double)zz,x--,y--,map[x][y][++num[x][y]]=z,map[y][x][++num[y][x]]=z; for (i=0;i<n;i++) for (j=0;j<n;j++) if (num[i][j]) { for (k=1;k<=num[i][j];k++) R[i][j]+=(double)1.0/map[i][j][k]; R[i][j]=1.0/R[i][j]; } ans[0]=INF;ans[n-1]=0;N=n-2; for (i=1;i<=N;i++) { if (R[i][0]) f[i][i]-=1.0/R[i][0],s[i]-=ans[0]/R[i][0]; if (R[i][n-1]) f[i][i]-=1.0/R[i][n-1]; for (j=1;j<=N;j++) if (R[i][j]&&i!=j) f[i][j]=1.0/R[i][j],f[i][i]-=1.0/R[i][j]; } for (i=1;i<N;i++) { for (j=i+1;j<=N;j++) { temp=f[j][i]/f[i][i]; for (k=i;k<=N;k++) f[j][k]-=f[i][k]*temp; s[j]-=s[i]*temp; } } for (i=N;i;i--) { for (j=i+1;j<=N;j++) s[i]-=ans[j]*f[i][j]; ans[i]=s[i]/f[i][i]; } for (i=0;i<=N;i++) if (R[i][n-1]) A+=ans[i]/R[i][n-1]; printf("%.2lfn",(INF/A+1e-4)); } return 0;}
