#include<stdio.h>
int n,m,i,x[1771],y[1771],c[1771],pol[61],pp,pm,sol;
int main()
{       FILE *f,*g;f=fopen("traseu.in","r");g=fopen("traseu.out","w");
	fscanf(f,"%ld%ld",&n,&m);
	for(i=1;i<=m;i++){fscanf(f,"%ld%ld%ld",&x[i],&y[i],&c[i]);
	pol[x[i]]++;pol[y[i]]--;}
	for(i=1;i<=n;i++)
	{if(pol[i]>0)pp+=pol[i];
	 else pm+=pol[i];}
         if(pp+pm)for(;;);
	fprintf(g,"%ld\n",sol);
	return 0;
}