#include <cstdio>

#define Nmax 260
int n, m, i, j, a, b, c, k;
int V[Nmax][Nmax], grad[Nmax];
double cc;
double D[Nmax], G[Nmax][Nmax], X[Nmax];

void citire () {
	
	FILE *f = fopen ("tunel.in", "r");	
	fscanf (f, "%d %d", &n, &m);
	
	for (i = 1; i <= m; i++) {
		fscanf (f, "%d %d %d", &a, &b, &c);
		V[a][b]++; V[b][a]++; grad[a]++; grad[b]++;
		D[a]+= c; D[b]+=c;
	}
	
	fclose (f);
}

void solve () {

	// grad[nod] * x[nod] -  V[nod][fiu1] * x[fiu1] - ... - V[nodk][fiu] * x[fiuk] = D[nod];
	for (i = n - 1; i >= 1; i--) {
		for (j = 1; j < n; j++)
			G[i][j] = -V[i][j];
		
		G[i][i] = grad[i];
	}
	
	for (i = 1; i < n; i++) 
		for (j = i+1; j < n; j++) 
			if (G[j][i] ) { // G[i][i] != 0 (grad[i] != 0)
				cc = - G[i][i] / G[j][i];
				for (k = i; k < n; k++) {
					G[j][k] = G[j][k] * cc + G[i][k];
				}
				
				D[j] = D[j] * cc + D[i]; 
			}
	
	
	X[n-1] = D[n-1] / G[n-1][n-1];
	for (i = n-2; i >= 1; i--) {
		cc = 0;
		for (j = i + 1; j < n; j++)
			cc+= G[i][j] * X[j];
		
		X[i] = (D[i] - cc) / G[i][i];
	}
	
}

int main () {
	
	citire ();
	solve ();
	
	FILE *g = fopen ("tunel.out", "w");
	fprintf (g, "%lf", X[1]);
	fclose (g);
	
	return 0;
}