#define F(k,v)d[j]>d[j+k]+v&&(d[j]=d[j+k]+v)
d['@@'];main(n,p,j,a,b,c){scanf("%d%d",&n,&p);for(d[p+1]=d[p+2]=d[p+3]=j=1e9;j++<p||(j=0,~scanf("%d%d%d",&a,&b,&c));F(1,b),F(2,c),F(3,1))d[j]+=a;n=!printf("%f",1.**d/n);}