ll@n,@m,a[m],b[];
double c[],d[n]{},e[];
rd((a,b,c)(m));
d[a[0..m-1]]+=c[0..];
c[0..m-1]/=d[a[0..]];
d[0..n-1]=10;
rep(100){
	rep(j,n){
		e[j]=d[j];
		d[j]=0;
	}
	rep(i,m){
		d[b[i]]+=e[a[i]]*c[i];
	}
}
wtLn(d(n));