#include <bits/stdc++.h>

#define fst(t) std::get<0>(t)
#define snd(t) std::get<1>(t)
#define thd(t) std::get<2>(t)
#define unless(p) if(!(p))
#define until(p) while(!(p))

using ll = std::int64_t;
using P = std::tuple<int,int>;

int N, M, A;
std::vector<P> v[100100];
ll dp[100100][2];

ll rec(int x, bool has){
    if(x == 0){
        return 0;
    }

    if(dp[x][has] != -1){
        return dp[x][has];
    }

    ll mx = rec(x - 1, 0);
    
    for(auto &pa : v[x]){
        int l, p;
        std::tie(l, p) = pa;

        mx = std::max(mx, rec(l, 1) + (has ? 0 : -A) + (l == 0 ? 0 : -A) + p);
    }

    return dp[x][has] = mx;
}

int main(){
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    std::cin >> N >> M >> A;

    for(int i=0;i<M;++i){
        int l, r, p;
        std::cin >> l >> r >> p;

        l -= 1;
        r -= 1;

        v[r+1].emplace_back(l, p);
    }

    memset(dp, -1, sizeof(dp));

    ll mx = rec(N, 1);
    std::cout << mx << std::endl;
}