#include "bits/stdc++.h"
using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) printf(__VA_ARGS__)

int dxy[] = {0, 1, 0, -1, 0};

/*================================*/

int N, M, A;
struct Range {
    int l;
    int r;
    int p;
};
map<int, vector<Range>> MAP;

signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    cin >> N >> M >> A;
    int dp[N+1];
    REP(i, M) {
        Range range = *new Range();
        cin >> range.l >> range.r >> range.p;
        range.l--;
        MAP[range.r].push_back(range);
    }
    int maxScore = dp[0] = 0;
    REP(i, N+1) {
        if (i == 0) continue;
        dp[i] = maxScore - A;
        for (auto r: MAP[i]) {
            int score = dp[r.l] + r.p;
            if (i != N) score -= A;
            dp[i] = max(dp[i], score);
        }
        maxScore = max(maxScore, dp[i]);
    }
    cout << maxScore << endl;
    
    return 0;
}