const INF: isize = 1isize << 60;

fn main() {
    let mut nma = String::new();
    std::io::stdin().read_line(&mut nma).ok();
    let nma: Vec<usize> = nma.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nma[0];
    let m = nma[1];
    let a = nma[2] as isize;
    let mut lines = (0..m).map(|_| {
            let mut temp = String::new();
            std::io::stdin().read_line(&mut temp).ok();
            let temp: Vec<usize> = temp.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
            (temp[0]-1, temp[1], temp[2] as isize)
        })
        .collect::<Vec<_>>();

    let mut dp = vec![vec![-INF; 2]; n+1];
    for i in 0..=n { dp[i][0] = 0; }
    dp[0][1] = 0;
    let mut lidx = 0usize;
    for &(l, r, p) in lines.iter() {
        while lidx < l {
            dp[lidx+1][0] = dp[lidx+1][0].max(dp[lidx][0]).max(dp[lidx][1]);
            lidx += 1;
        }
        let leftcost = if l == 0 { 0 } else { a };
        let rightcost = if r == n { 0 } else { a };
        dp[r][1] = dp[r][1].max(dp[l][0] - leftcost - rightcost + p).max(dp[l][1] - rightcost + p);
    }
    println!("{}", dp.iter().map(|v| v.iter().max().unwrap()).max().unwrap());
}