/* -*- coding: utf-8 -*-
 *
 * 496.cc: No.496 ワープクリスタル (給料日前編) - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 50;
const int MAX_X = 100, MAX_Y = 100;
const int INF = 1 << 30;

/* typedef */

/* global variables */

int cxs[MAX_N], cys[MAX_N], cs[MAX_N];
int dp[2][(MAX_Y + 1) * (MAX_X + 1)];

/* subroutines */

inline void setmin(int &a, int b) { if (a > b) a = b; }

/* main */

int main() {
  int gx, gy, n, f;
  cin >> gx >> gy >> n >> f;
  for (int i = 0; i < n; i++) cin >> cxs[i] >> cys[i] >> cs[i];

  int dn = (gy + 1) * (gx + 1);
  for (int i = 0; i < 2; i++) fill(dp[i], dp[i] + dn, INF);
  dp[0][0] = 0;
  int cur = 0, nxt = 1;

  for (int i = 0; i < n; i++) {
    copy(dp[cur], dp[cur] + dn, dp[nxt]);

    for (int y0 = 0, y1 = cys[i]; y1 <= gy; y0++, y1++)
      for (int x0 = 0, x1 = cxs[i]; x1 <= gx; x0++, x1++) {
	int &d0 = dp[cur][y0 * (gx + 1) + x0];
	if (d0 < INF)
	  setmin(dp[nxt][y1 * (gx + 1) + x1], d0 + cs[i]);
      }

    cur ^= 1, nxt ^= 1;
  }

  int minc = INF;
  for (int y = 0, p = 0; y <= gy; y++)
    for (int x = 0; x <= gx; x++, p++)
      if (dp[cur][p] < INF)
	setmin(minc, dp[cur][p] + ((gx - x) + (gy - y)) * f);
  printf("%d\n", minc);
  return 0;
}