#include<stdio.h>
#include<algorithm>
#include<math.h>

using namespace std;

#define lg 260
#define eps 0.00001
#define a A

int n, m, x, y, z, i, j, k, sm[lg], grd[lg];
double A[lg][lg], aux;

double ab(double a){
	return a < 0 ? -a : a;
}

void print(double A[lg][lg]){
	for (int i = 1; i <= n; i ++){
		for (int j = 1; j <= n+1; j ++)
			printf("%lf ", A[i][j]);
		printf("\n");
	}
	printf("\n\n");
}

int main()
{
	freopen("tunel.in", "rt", stdin);
	freopen("tunel.out", "wt", stdout);

	scanf("%d%d", &n, &m);
	for (i = 1; i <= m; i ++){
		scanf("%d%d%d", &x, &y, &z);

		grd[x] ++, grd[y] ++; sm[x] += z, sm[y] += z;
		A[x][y] ++, A[y][x] ++;
	}

	for (i = 1; i < n; i ++){
		A[i][n+1] = sm[i] / grd[i];
		A[i][n+1] *= -1;

		for (j = 1; j <= n; j ++)
			A[i][j] /= grd[i];
		A[i][i] -= 1;
	}

	memset(A[n], 0, sizeof(A[n]));
	A[n][n] = 1, A[n][n+1] = 0;

	//print(A);

	for (i = 1; i <= n; i ++){
		if (ab(A[i][i]) < eps)
			for (j = i; j <= n; j ++)
				if (ab(A[j][i]) > eps){
					for (k = 1; k <= n+1; k ++)
						swap(A[i][k], A[j][k]);
					break;
				}

		if (ab(A[i][i]) < eps)
			break;
		aux = 1 / A[i][i];
		for (j = 1; j <= n+1; j ++)
			A[i][j] *= aux;

		for (j = 1; j <= n; j ++)
			if (i != j){
				aux = A[j][i] / A[i][i];
				for (k = i; k <= n+1; k ++)
					A[j][k] -= aux * A[i][k];
			}
	}
	
	//print(A);

	printf("%.3lf\n", A[1][n+1] / A[1][1]);

	return 0;
}