import std.stdio, std.conv, std.functional, std.string;
import std.algorithm, std.array, std.container, std.range, std.typecons;
import std.numeric, std.math, std.random;
import core.bitop;

string FMT_F = "%.10f";

static string[] s_rd;
T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
string RDR()() { return readln.chomp; }
T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; }
size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
long lcm(long x, long y) { return x * y / gcd(x, y); }

long mod = 10^^9 + 7;
//long mod = 998244353;
//long mod = 1_000_003;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }

void main()
{
	auto N = RD;
	auto M = RD;
	auto A = RD;
	auto lrp = new long[][](M, 3);
	foreach (i; 0..M)
	{
		lrp[i] = [RD-1, RD-1, RD];
		/*if (lrp[i][0] != 0)
			lrp[i][2] -= A;
		if (lrp[i][1] != N-1)
			lrp[i][2] -= A;*/
	}
	lrp.sort!"a[0] < b[0]"();

	auto dp = new long[][](N+1, 2);
	size_t li;
	foreach (i; 0..N)
	{
		if (dp[i][0] > dp[i+1][0])
			dp[i+1] = dp[i].dup;
		
		if (li == M) continue;
		while (lrp[li][0] == i)
		{
			auto r = lrp[li][1];
			auto p = lrp[li][2];
			if (dp[i][1] != i)
				p -= A;
			if (r != N-1)
				p -= A;

			if (dp[i][0] + p > dp[r+1][0])
			{
				dp[r+1] = [dp[i][0]+p, r+1];
			}
			++li;
			if (li == M) break;
		}
	}

	writeln(dp[N][0]);
	stdout.flush();
	debug readln();
}