#include <bits/stdc++.h>

using namespace std;

vector <pair<int,int>> adj[100005];
long long int dp[100005];

int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    int n,m,a,l,r,p;

    cin >> n >> m >> a;

    for(int i=0;i<m;i++)
    {
        cin >> l >> r >> p;
        adj[l].push_back(make_pair(r,p));
    }

    for(int i=0;i<=n;i++)
    {
        dp[i] = -1e18;
    }

    dp[0] = 0;

    long long int Max = 0;
    int idx = 0;


    for(int i=1;i<=n;i++)
    {
        for(auto it : adj[i])
        {
            int j = it.first;
            int get = it.second;
            if(idx==i-1)
            {
                if(j==n)
                {
                    dp[j] = max(dp[j],get + Max);
                }
                else
                {
                    dp[j] = max(dp[j],get + Max - a);
                }
            }
            else
            {
                if(j==n)
                {
                    dp[j] = max(dp[j], get + Max);
                }
                else
                {
                    dp[j] = max(dp[j],get + Max - a);
                }
            }
        }
        Max -= a;
        if(Max <= dp[i])
        {
            Max = dp[i];
            idx = i;
        }
    }

    cout << Max << '\n';

    return 0;
}