#include <bits/stdc++.h>
#define fi first
#define se second
#define ll long long
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pill pair<int,ll>
#define mem(a, b) memset(a, b, sizeof(a))
#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1)
#define name "test"
using namespace std;
const int N = 1e5 + 5;
const int mod = 1e9 + 7;
const ll oo = 1e18;
template <typename T1, typename T2> bool maxi(T1 &a, T2 b){if (a < b){a = b; return 1;} return 0;}
template <typename T1, typename T2> bool mini(T1 &a, T2 b){if (a > b){a = b; return 1;} return 0;}
bool ok;
struct SEGTREE{
ll val[N << 2];
SEGTREE(){
mem(val, -0x3f);
};
void update(int id, int l, int r, int i, ll x){
if (l > i || r < i) return;
if (l == r){
val[id] = max(val[id], x);
return;
}
int m = (l + r) >> 1;
if (m >= i) update(id << 1, l, m, i, x);
else update(id << 1 | 1, m + 1, r, i, x);
val[id] = max(val[id << 1], val[id << 1 | 1]);
}
ll get(int id, int l, int r, int u, int v){
if (l > v || r < u) return -oo;
if (l >= u && r <= v) return val[id];
int m = (l + r) >> 1;
return max(get(id << 1, l, m, u, v), get(id << 1 | 1, m + 1, r, u, v));
}
} ST;
int s, t;
int limDis, downPower, n;
int a[N];
int b[N];
ll ans = -oo;
vector <int> value;
void load(){
cin.tie(0)->sync_with_stdio(0);
if (fopen(name".inp", "r")){
freopen(name".inp", "r", stdin);
freopen(name".out", "w", stdout);
}
}
void input(){
cin >> s >> t >> limDis >> downPower >> n;
for (int i = 1; i <= n; i++)
cin >> a[i] >> b[i];
}
void solve(){
a[0] = s;
a[n + 1] = t;
for (int i = 0; i <= n + 1; i++){
int r = a[i] % limDis;
if (r == 0) r = limDis;
value.push_back(r);
}
sort(value.begin(), value.end());
int nSeg = value.size();
int r = s % limDis;
ll k = (s + limDis - 1) / limDis;
if (r == 0) r = limDis;
int id = lower_bound(value.begin(), value.end(), r) - value.begin() + 1;
ST.update(1, 1, nSeg, id, k * downPower);
for (int i = 1; i <= n + 1; i++){
int r = a[i] % limDis;
ll k = (a[i] + limDis - 1) / limDis;
if (r == 0) r = limDis;
int id = lower_bound(value.begin(), value.end(), r) - value.begin() + 1;
ll tmp1 = ST.get(1, 1, nSeg, 1, id - 1) - k * downPower - downPower + b[i];
ll tmp2 = ST.get(1, 1, nSeg, id, nSeg) - k * downPower + b[i];
if (i == n + 1) maxi(ans, max(tmp1, tmp2));
ST.update(1, 1, nSeg, id, max(tmp1, tmp2) + k * downPower);
}
cout << ans;
}
int main(){
load();
input();
solve();
}
