#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using ll =  long long ;
using P = pair<int,int> ;
const ll INF = 1e18;
const int MOD = 1000000007;

int main(){
    int n,m,a;
    cin >> n >> m >> a;
    vector<vector<ll>> section(m,vector<ll>(3,0));
    vector<int> before(m,-1);
    vector<P> dp(m+1);
    rep(i,m){
        ll l,r,p;
        cin >> l >> r >> p;
        --l;
        section[i][0] = r;
        section[i][1] = l;
        section[i][2] = p;
    }
    sort(section.begin(),section.end());
    rep(i,m){
        int l = -1,r = i;
        while(r - l > 1){
            int mid = (l+r)/2;
            if(section[mid][0] <= section[i][1]) l = mid;
            else r = mid;
        }
        before[i] = l;
    }
    dp[0] = P(0,0);
    for(int i=1;i<=m;i++){
        dp[i] = dp[i-1];
        if(before[i-1] == -1){
            ll res = section[i-1][2];
            int c = 2;
            if(section[i-1][1] == 0) --c;
            if(section[i-1][0] == n) --c;
            res -= a * c;
            if(res >= dp[i].first){
                dp[i] = P(res,section[i-1][0]);
            }
        }
        else{
            ll res = dp[before[i-1]+1].first + section[i-1][2];
            int c = 2;
            if(dp[before[i-1]+1].second == section[i-1][1]) --c;
            if(section[i-1][0] == n) --c;
            res -= c * a;
            if(res >= dp[i].first){
                dp[i] = P(res,section[i-1][0]);
            }
        }
    }

    //rep(i,m) cout << section[i][0] << " "  << section[i][1] << " " << section[i][2] << endl;
    //rep(i,m) cout << before[i] << " " << endl;
    //rep(i,m+1) cout << dp[i].first << " " << dp[i].second << endl;
    cout << dp[m].first << endl;
    return 0;
}