using System;
using System.Collections.Generic;
using System.IO;
class Solution {
    
    static void Main(String[] args) {
        
        string[] inString = Console.ReadLine().Split(' ');
        uint[] initParams = Array.ConvertAll(inString, UInt32.Parse);
        uint n = initParams[0];
        uint m = initParams[1];
        
        long[] numList = new long[n+1];
        
        for(int i=0; i<m; i++)
        {
            string[] opString = Console.ReadLine().Split(' ');
            uint a = UInt32.Parse(opString[0]);
            uint b = UInt32.Parse(opString[1]);
            long k = long.Parse(opString[2]);
            
            numList[a] += k;
            if(b+1 <= n) numList[b+1] -= k;
        }
        
        long tempMax = 0;
        long max = 0;
        for(int i=1; i<=n; i++)
        {
            tempMax += numList[i]; 
            if(tempMax > max) max = tempMax;
        }
        
        Console.WriteLine(max.ToString());
    }
}