#include<cstdio>
#include<vector>
using namespace std;
typedef pair<int,int> PII;
vector<PII> nr[260];
int N,M,grad[260];
double G[260][260];
void init(){
	for(int i=1;i<N;++i){
		G[i][i]=grad[i];
		for(vector<PII>::iterator it=nr[i].begin();it!=nr[i].end();++it){
			--G[i][it->first];
			G[i][N+1]+=it->second;
		}
	}
	G[N][N]=1;
	G[N][N+1]=0;
}
void solve(){
	init();
	int i,j,k;
	for(i=1;i<=N;++i){
		for(j=i+1;j<=N;++j){
			for(k=N+1;k>=i;--k){
				if(G[j][i]){
					G[j][k]-=G[j][i]/G[i][i]*G[i][k];
				}
			}
		}
	}
	for(j=N;j;--j){
		G[j][N+1]/=G[j][j];
		G[j][j]=1;
		for(i=j-1;i;--i){
			G[i][N+1]-=G[i][j]*G[j][N+1];
			G[i][j]=0;
		}
	}
}
int main(){
	freopen("tunel.in","r",stdin);
	freopen("tunel.out","w",stdout);
	int i,x,y,c;
	scanf("%d%d",&N,&M);
	for(i=0;i<M;++i){
		scanf("%d%d%d",&x,&y,&c);
		++grad[x];
		++grad[y];
		nr[x].push_back(PII(y,c));
		nr[y].push_back(PII(x,c));
	}
	solve();
	printf("%.4lf\n",G[1][N+1]);
	
	fclose(stdin);
	fclose(stdout);
	return 0;
}