#include <bits/stdc++.h>
using namespace std;
using i64=int_fast64_t;
using pii=pair<int,int>;
template <class T> constexpr T inf=numeric_limits<T>::max() / (T)2;
template <class T> using minheap=priority_queue<T,vector<T>,greater<T>>;
#define fir first
#define sec second
#define mkp make_pair
#define mkt make_tuple
#define emb emplace_back
#define all(v) begin(v),end(v)
i64 binry(i64 ok, i64 ng, const function<bool(i64)> &f) {
    while(abs(ok-ng)>1) {
        i64 mid=(ok+ng)/2;
        (f(mid) ? ok : ng) = mid;
    }
    return ok;
}

int n,m,A;
vector<pii> segs[1<<17];
i64 dp[1<<17];

signed main() {
    cin>>n>>m>>A;
    for(int i=0; i<m; ++i) {
        int l,r,p; cin>>l>>r>>p;
        segs[r-1].emplace_back(l-1,p);
    }
    fill(dp,dp+n+2,-inf<i64>);
    dp[0]=0;
    for(i64 i=0,rui=0; i<n; ++i) {
        int dec=A;
        if(i==n-1) dec=0;
        dp[1+i]=max(dp[i+1],rui-dec);
        for(auto &s:segs[i]) {
            int l,p; tie(l,p)=s;
            dp[i+1]=max(dp[1+i],dp[l]+p-dec);
        }
        rui=max(rui,dp[i+1]);
    }
    cout<<dp[n]<<"\n";
}