#define F(k,v)d[j]>d[j+k]+v&&(d[j]=d[j+k]+v)
d['@@'];n;main(p,j,a,b,c){scanf("%d%d",&n,&p);for(memset(d+p+1,99,12);j++<p||~scanf("%d%d%d",&a,&b,&c,j=0);F(1,b),F(2,c),F(3,1))d[j]+=a;n=!printf("%f",1.**d/n);}