#include <stdio.h>
#include <iostream>
#include <string.h>
#include <math.h>
#include <algorithm>
using namespace std;
const int M = 10005;
struct grid{
    int t,r,c;
}g[M];
int dp[M];
int cmp(grid a,grid b){
    return a.t < b.t;
}
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF,n+m){
        for(int i=1;i<=m;i++){
            scanf("%d%d%d",&g[i].t,&g[i].r,&g[i].c);
        }
        sort(g+1,g+m+1,cmp);
        int ans = -1;
        for(int i=1;i<=m;i++){
            dp[i]=1;
            for(int j=1;j<i;j++){
                int usetime = abs(g[i].r-g[j].r)+abs(g[i].c-g[j].c);
                if(usetime<=abs(g[j].t-g[i].t)&&dp[j]+1>dp[i]) dp[i] = dp[j]+1;
            }
            ans = max(ans,dp[i]);
        }
        printf("%d\n",ans);
    }
    return 0;
}