#include <bits/stdc++.h>
#define fi first
#define se second
#define maxn 100005
using namespace std;
using ii = pair<int, int>;
int K, M, D, A, N;
int64_t dp[maxn];
ii a[maxn];
int64_t st[4*maxn];
int b[maxn], n1 = 0;
void upd(int u, int64_t d, int r = 1, int lo = 1, int hi = n1) {
if (lo == hi) {
st[r] = max(st[r], d);
return;
}
int mid = (lo + hi) >> 1;
if (u <= mid) upd(u, d, r<<1, lo, mid);
else upd(u, d, r<<1|1, mid+1, hi);
st[r] = max(st[r<<1], st[r<<1|1]);
}
int64_t get(int u, int v, int r = 1, int lo = 1, int hi = n1) {
if (u > hi || v < lo) return LLONG_MIN/2;
if (u <= lo && hi <= v) return st[r];
int mid = (lo + hi) >> 1;
return max(get(u, v, r<<1, lo, mid), get(u, v, r<<1|1, mid+1, hi));
}
void update(int pos, int64_t val) {
int p = lower_bound(b + 1, b + n1 + 1, pos%D) - b;
upd(p, val);
}
int main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
cin >> K >> M >> D >> A >> N;
b[++n1] = K%D; b[++n1] = M%D;
for (int i = 1; i <= N; i++) {
cin >> a[i].fi >> a[i].se;
b[++n1] = a[i].fi%D;
}
sort(b + 1, b + n1 + 1);
n1 = unique(b + 1, b + n1 + 1) - b - 1;
for (int i = 1; i <= 4 * n1; i++) st[i] = LLONG_MIN/2;
update(K, 1LL*(K/D)*A);
a[++N] = {M, 0};
for (int i = 1; i <= N; i++) {
auto [T, B] = a[i];
int p = lower_bound(b + 1, b + n1 + 1, T%D) - b;
dp[i] = max(get(1, p) - A, get(p, n1)) - int64_t(1) * (T/D) * A + B;
update(T, dp[i] + 1LL * (T/D) * A);
}
cout << dp[N];
}
