#include <bits/stdc++.h>
#define LINF 1000000000000000000LL
using namespace std;
typedef long long ll;
ll t[101010];
ll tree[804040], b[101010], dp[101010];
vector <ll> num;
ll update(ll node, ll s, ll e, ll k, ll val) {
if(s == e) return tree[node] = max(tree[node], val);
ll m = (s+e)>>1;
if(k <= m) tree[node] = max(tree[node*2+1], update(node*2, s, m, k, val));
else tree[node] = max(tree[node*2], update(node*2+1, m+1, e, k, val));
return tree[node];
}
ll cal(ll node, ll s, ll e, ll l, ll r) {
if(s > r || e < l) return -LINF;
if(s >= l && e <= r) return tree[node];
ll m = (s+e)>>1;
return max(cal(node*2, s, m, l, r), cal(node*2+1, m+1, e, l, r));
}
int main() {
ios::sync_with_stdio(false); cin.tie(0);
ll K, M, D, n;
ll A;
cin >> K >> M >> D >> A >> n;
M -= K;
for(ll i = 1; i <= n; i++) {
cin >> t[i] >> b[i];
t[i] -= K;
num.push_back(t[i] % D);
}
num.push_back(M % D);
t[n+1] = M;
sort(num.begin(), num.end());
for(ll i = 0; i < 804040; i++) tree[i] = -LINF;
update(1, 0, num.size()-1, 0, 0LL);
for(ll i = 1; i <= n+1; i++) {
ll k = lower_bound(num.begin(), num.end(), t[i] % D) - num.begin();
dp[i] = max(cal(1, 0, num.size()-1, 0, k-1) - A, cal(1, 0, num.size()-1, k, num.size()-1)) + b[i];
update(1, 0, num.size()-1, k, dp[i]);
}
cout << dp[n+1] - A * (M / D);
}
