#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <deque>
#include <queue>
#include <array>
#include <set>
#include <map>
#include <cmath>
#include <algorithm>
#include <numeric>
#include <cassert>
#include <utility>
#include <tuple>
#include <functional>
#include <bitset>
#include <cstdint>

using namespace std;
using i64 = int64_t;
using i32 = int32_t;
template<class T, class U> void init_n(vector<T>& v, size_t n, U x) 
{ v = vector<T>(n, x); }
template<class T> void init_n(vector<T>& v, size_t n) { init_n(v, n, T()); }
template<class T> void read_n(vector<T>& v, size_t n, size_t o = 0) 
{ v = vector<T>(n+o); for (size_t i=o; i<n+o; ++i) cin >> v[i]; }
template<class T> void read_n(T a[], size_t n, size_t o = 0)
{ for (size_t i=o; i<n+o; ++i) cin >> a[i]; }
template<class T> T gabs(const T& x) { return max(x, -x); }
#define abs gabs

int main() {
  i64 n, m, a;
  cin >> n >> m >> a;
  vector<tuple<i64, i64, i64>> s;
  for (i64 i = 0; i < m; ++i) {
    i64 l, r, p;
    cin >> l >> r >> p;
    s.emplace_back(l, r, p);
  }
  sort(begin(s), end(s));
  vector<array<i64, 2>> dp(n + 2);
  for (i64 i = 1; i <= n; ++i) dp[i][1] = -(1ll << 51);
  for (i64 i = 1, j = 0; i <= n; ++i) {
    dp[i][0] = max(dp[i - 1][0], dp[i - 1][1]);
    for (; j < m && get<0>(s[j]) == i; ++j) {
      i64 l, r, p;
      tie(l, r, p) = s[j];
      i64 b = r == n ? 0 : a;
      dp[r][1] = max({
        dp[r][1], p + dp[l - 1][1] - b, p + dp[l - 1][0] - a - b
      });
    }
  }
  cout << max(dp[n][0], dp[n][1]) << '\n';
  return 0;
}